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 American Journal of  
Food Science and Technology (AJFST)

Evaluation of  the Nutritional Profile and Obesogenic Potential of  a Formulated High-
Fat Diet

Edith Reuben1, Bruno Chukwuemeka Chinko2*, Nimisoere Peace Batubo1, Precious Whiskey Ikete3, Fortune Somiari Amah-Tariah1

Volume 4 Issue 2, Year 2025
ISSN: 2834-0086 (Online)

DOI: https://doi.org/10.54536/ajfst.v4i2.5213
https://journals.e-palli.com/home/index.php/ajfst

Article Information ABSTRACT

Received: April 28, 2025

Accepted: June 02, 2025

Published: October 14, 2025

High-fat diets (HFDs) are commonly used in nutritional research to model obesity and 
associated metabolic disorders. However, detailed profiling of  their nutritional composition 
and physiological effects is essential for model validation. The present study developed 
standardized HFDs using locally available beef  tallow as a cost-effective fat source and 
evaluated both the nutritional profile of  these formulated diets and their efficacy in promoting 
obesity progression using male Wistar rat models. Fifteen (15) male Wistar rats were locally 
sourced and used for the study. They were grouped into three (3) of  five (5) animals each. 
Group I served as the control and received standard rat chow (SRC) while groups II and 
IIIreceived SRC blended with 10% (HF-10) and 20% (HF-20) beef  tallow respectively. The 
experiment lasted for ten (10) weeks during which all the animals were allowed access to feed 
and water ad libitum. Proximate analysis of  the rat diets and faecal matter were determined 
using standard methods. Feed efficiency, nutrient digestibility, and morphometric parameters 
were determined using standard formula. Results from the study indicate that protein and 
fibre content of  the rats’ feed was reduced with increased fat supplementation with the HF-
20 rat showing the highest energy (4144.1 Kcal/kg) and 64.8% increase in feed efficiency 
compared to the SRC diet. Also, HF diets increased body weight (35%), Lee’s obesity index 
(18.5%), abdominal circumference (43.5%), absolute adipose tissue weight (776.43%) and 
adiposity index (529.2%) in a dose-dependent manner. The faecal proximate composition 
analysis showed a slight increase in ash and lipid excretion with an enhanced fat digestibility 
coefficient. Evidence from the present study shows that a high-fat diet containing 20% beef  
tallow (HF-20) effectively induced obesity and associated metabolic disturbances in male 
Wistar rats. The findings demonstrate a clear dose-response relationship between dietary fat 
content and the development of  obesity-related phenotypes. These findings highlight the 
use of  HFD in understanding the pathophysiology of  obesity and metabolic disease, while 
also providing a practical animal obesity model for preclinical research.

Keywords

Feed Efficiency, High-fat Diet, 
Nutrient Digestibility, Obesity, 
Proximate Analysis

1 Department of  Human Physiology, Faculty of  Basic Medical Sciences, College of  Medical Sciences, Rivers State University, Port 
Harcourt, Nigeria.
2 Department of  Human Physiology, Faculty of  Basic Medical Sciences, College of  Health Sciences, University of  Port Harcourt, 
Port Harcourt, Nigeria.
3 Department of  Human Physiology, Faculty of  Basic Medical Sciences, College of  Health Sciences, Federal University Otuoke, 
Nigeria
* Corresponding author’s e-mail: bruno.chinko@uniport.edu.ng

INTRODUCTION
Obesity is a chronic metabolic disorder characterized by 
an abnormal or excessive accumulation of  body fat that 
adversely affects health. Recognized as a global epidemic 
by the World Health Organization (OECD/WHO, 
2024; WHO, 2025). It is a leading risk factor for non-
communicable diseases (NCDs) and represents a global 
public health crisis, with prevalence increasing across high, 
low, and middle-income countries (Azeez, 2022; Islam 
et al., 2024). Obesity is a complex, metabolic, chronic, 
progressive, neurobehavioral disorder characterized 
by an increase in adiposity, which promotes adipose 
tissue dysfunction and abnormal deposition of  fat 
mass resulting in adverse metabolic, biomechanical, and 
psychosocial health concerns (Brown et al., 2024; Ikete 
& Chinko, 2022). It is associated with increased risks for 
several comorbidities, such as insulin resistance, type 2 
diabetes, dyslipidaemia, hypertension, cardiovascular 
diseases, atherosclerotic cerebrovascular disease, chronic 
liver disease, gallbladder disease, colorectal cancer, 

osteoarthritis, psychosocial problems as well as a higher 
mortality rate (Zhang et al., 2014). The development of  
obesity primarily arises from a chronic energy imbalance, 
characterized by sustained caloric intake exceeding energy 
expenditure. This imbalance is influenced by factors such 
as excessive energy consumption, physical inactivity, and 
genetic predisposition (Bays et al., 2024; Billington et al., 
2000; Kopelman, 2000; Showalter et al., 2018). While the 
aetiology of  obesity is multifactorial, a prolonged positive 
energy balance remains a widely accepted mechanism 
underlying its pathogenesis. Notably, excessive energy 
intake has been identified as a key driver of  obesity, with 
studies suggesting it may play a predominant (if  not 
exclusive) role in weight gain (Bays et al., 2024; Hu et al., 
2018).
Long-term management and prevention of  obesity rely 
on lifestyle modifications, including diet and physical 
activity, while pharmacological and surgical interventions 
may be necessary in severe cases to achieve substantial 
weight loss (Encinosa et al., 2005; Ikete & Chinko, 



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Am. J. Food. Sci. Technol. 4(2) 34-43, 2025

2022; Kushner, 2014). These interventions are enabled 
by research utilizing experimental models of  obesity 
primarily rodents, to mimic human obesity and its 
metabolic complications (Hariri & Thibault, 2010). 
High-fat diets (HFDs) are well-established inducers of  
obesity in both humans and animal models reinforcing 
that obesity primarily arises from excessive energy 
consumption (Coelho et al., 2011; Folorunso et al., 2020), 
with a dose-dependent relationship between dietary 
fat content and increased body weight or adiposity (de 
Wit et al., 2011; Enos et al., 2013). The HFD used in 
experimental obesity models, typically comprises 40–
60% of  total caloric intake from fats with the type of  fat, 
carbohydrate content, and protein sources significantly 
influencing metabolic outcomes (An et al., 2022; Wali et 
al., 2020). Lard and beef  tallow, which are rich in saturated 
fatty acids (SFAs), are commonly used fat sources in high-
fat diets (HFDs). Alternatively, plant-derived oils such as 
corn and safflower oil which are high in polyunsaturated 
fatty acids (PUFAs) are also employed in the experimental 
formulation of  HFDs (Showalter et al., 2018; Wali et al., 
2020). These diets exhibit higher energy density compared 
to standard rodent chow due to their elevated fat content, 
which contributes to their obesogenic properties (Sadie-
Van Gijsen & Kotzé-Hörstmann, 2023). 
The reliance on expensive commercial HFDs or 
nutritionally incomplete formulations presents major 
challenges for obesity research, particularly in resource-
limited settings where diet-induced metabolic disorders 
are increasingly prevalent. Developing standardized yet 
affordable HFDs using regionally available fat sources 
could address both the nutritional inadequacies of  
current commercial formulations and the accessibility 
limitations of  prepackaged diets. The present study is 
therefore aimed at formulating a standardising an HFD 
using locally and commonly available beef  tallow and 
evaluating the nutritional composition of  the HFD and 
monitoring its progression on induction of  obesity using 
male Wistar rat models. This may lead to the development 
of  evidence-based, standardized high-fat diets (HFDs) 
that are both cost-effective and nutritionally complete 
using locally available ingredients. This formulation could 
significantly improve the accessibility and reproducibility 
of  formulated HFDs, particularly in low-income research 
settings, where the prohibitive expense of  imported, 
commercial obesogenic diets often restrict experimental 
capacity. 

MATERIALS AND METHODS
Research Animals
Fifteen (15) male Wistar rats, 120-130g, were sourced 
from the animal house of  the Department of  Human 
Physiology, University of  Port Harcourt, and used for the 
study. Males were selected to eliminate potential hormonal 
variations from the oestrous cycle that influence energy 
metabolism and to avoid inherent sex differences in body 
composition as females typically exhibit higher adiposity. 
The rats were maintained in well-ventilated wooden 

cages under controlled conditions (12:12 hr light-dark 
cycle; 28-31°C; 45-50% humidity) with ad libitum access 
to standard rat chow (SRC) and water. The floor of  the 
cages was lined with sawdust and cleaned daily. The 
animals were allowed two (2) weeks of  acclimatization 
before the commencement of  the study.

Formulation of  high-fat diet
The experimental high-fat diet was prepared following 
the previously described protocol from our centre (Alor 
& Chinko, 2022) with modifications to the preparation 
schedule. Fresh beef  tallow was acquired from a local 
abattoir in the Aluu community, Rivers State under strict 
hygienic conditions immediately post-slaughter to ensure 
quality and minimize oxidation. The tallow was washed; 
impurities and bone particles were removed. It was then 
boiled and allowed to cool before the fat was removed 
and refrigerated until the time for use. The beef  tallow 
was weighed using a digital weighing scale and melted 
before mixing with commercially standard rat chow. 
Two distinct high-fat diets (HFD) formulations were 
prepared: the first comprised 90% standard rat chow 
(SRC) supplemented with 10% beef  tallow (HF-10), 
while the second consisted of  80% standard chow (SRC) 
blended with 20% beef  tallow (HF-20). The obesogenic 
diets were prepared daily to avoid rancidity.

Experimental Design
The fifteen (15) male Wistar rats were randomly into 
three (3) groups of  five (5). Group I served as the control 
and received SRC and water ad libitum while groups II 
and IIIreceived HF-10 and HF-20 respectively alongside 
water ad libitum. The experimental procedure lasted for 
ten (10) weeks. 

Feed Analysis and Calorific Content
The proximate analysis of  the SRC (Apple and Pears, 
Ogun State Nigeria Ltd.), HF-10 and HF-20 diets was 
conducted at the Department of  Biochemistry, Faculty 
of  Science, University of  Port Harcourt. The calorific 
content was calculated by multiplying the weight of  each 
macronutrient by its respective energy density per gram: 
4 kcal/g for protein and carbohydrates and 9 kcal/g for 
fat (Food And Agriculture Organization of  The United 
Nations, 2003). The total caloric value was determined 
by summing the individual calorie contributions while 
the percentage of  calories from each macronutrient was 
derived by dividing its kilocalorie contribution by the total 
kilocalorie content and multiplying it by 100.

Proximate analysis 
Crude Protein Determination
Crude protein was determined using the micro-Kjeldahl 
method, which measures nitrogen as the characteristic 
element in protein rather than the protein itself. A 
mixture of  15 g of  potassium sulphate and 0.5 g of  
copper (II) sulphate was prepared in an 800 mL Kjeldahl 
flask. Approximately 2 g of  SRC, HF-10 and HF-20 



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Am. J. Food. Sci. Technol. 4(2) 34-43, 2025

were weighed (Mettler Toledo AB 204) and transferred 
into the flask, followed by the addition of  25 mL of  
concentrated sulphuric acid. The flask was swirled to mix 
the contents and then inclined on a heating device in a 
fume cupboard. Heating continued until foaming ceased 
and the contents liquefied. Gentle boiling was maintained 
using the digestion catalyst, with occasional rotation of  the 
flask, until the liquid turned clear and light blue. Digestion 
was continued for an additional 1.5 hours, ensuring a total 
digestion time of  at least 2 hours. The flask was then 
cooled to about 40°C, and 50 mL of  distilled water was 
cautiously added. After mixing, the solution was allowed 
to cool further. The digested solution was transferred into 
a 250 mL standard flask and rinsed several times to reach 
the mark. A 50 mL aliquot of  the digest was transferred to 
a steam distillation apparatus. In a separate conical flask, 25 
mL of  4% boric acid solution was prepared and positioned 
under the condenser, ensuring the outlet was submerged 
in the liquid. Then, 35 mL of  33% sodium hydroxide 
solution was added to the distillation flask, and steam 
distillation was carried out for 4 minutes after the first drop 
of  distillate or until the distillate was no longer alkaline. 
The conical flask was then lowered so that the condenser 
outlet was above the liquid level, and distillation continued 
for an additional minute. Next, four drops of  indicator 
solution (0.2 g methyl red and 0.1 g methylene blue in 100 
mL ethanol) were added to the distillate, which was then 
titrated with 0.1 M hydrochloric acid until a grey endpoint 
was reached. The analysis was repeated with a second 50 
mL portion of  the digest. A complete blank determination 
was also performed regularly for calibration.
% Nitrogen content = ((ml of  standard acid-ml of  blank) 
× N of  Acid × 1.4007)/(weight of  sample in grams)
Nitrogen was finally converted to crude protein by 
multiplying by 6.25 and expressed in g/100g.

Determination of  Moisture Content
Moisture content was determined by weighing the SRC, 
HF-10 and HF-20 in a porcelain crucible. The crucible 
with the sample was heated in an electric oven for about 
6 hours at 105°C. It was then cooled in a desiccator and 
weighed again.
% Moisture content = (weight of  moisture obtained 
(gm))/(weight of  sample (gm)) × 100

Determination of  Ash Content
The ash content was determined following the 
Association of  Official Analytical Chemists (AOAC) 
method. Approximately 2 g of  each sample (SRC, HF-10, 
and HF-20) was weighed in a pre-cleaned, pre-weighed 
crucible using an analytical balance (Mettler Toledo 
AB 204), and the initial weight was recorded. A muffle 
furnace was preheated and stabilized at 600°C. The 
weighed sample was evenly distributed in the crucible 
and carefully placed inside the furnace using tongs. The 
samples were ashed at the set temperature for 45 minutes 
to ensure complete combustion of  organic matter. After 
ashing, the crucible was removed from the furnace and 

transferred to a desiccator to cool, preventing moisture 
absorption before final weighing. The ashed sample on 
the crucible was weighed, and the percentage of  ash was 
determined using the formula: 
% Ash content = Weight of  Ash/Initial Weight of  
Sample ×100

Determination of  Crude Fibre
The crude fibre content was determined through a 
sequential extraction protocol. Approximately 2 g of  
each sample (SRC, HF-10, and HF-20) was mixed with a 
sulphuric acid solution (1.25%) and maintained at boiling 
temperature for 30 minutes to solubilize non-fibrous 
components. The resulting acid-insoluble residue was 
isolated through vacuum filtration using a Whatman 4 filter 
paper and washing with warm (60°C) distilled water until 
a neutral pH was achieved. The resulting residue was then 
mixed with 1.25% sodium hydroxide solution at boiling 
temperature for 30 minutes to remove proteinaceous and 
hemicellulosic materials. The alkali-treated residue was 
similarly filtered and washed to neutrality. The purified 
fibrous residue was then quantitatively transferred to 
a pre-weighed crucible and dried to constant mass at 
105±2°C in a forced-air oven (W1). To determine the 
inorganic contaminant fraction, the dried residue was then 
ashed in a muffle furnace at 550±25°C for 4 hours and 
recorded as (W2). The crude fibre content was calculated 
gravimetrically by subtracting the ash mass from the pre-
ashed residue mass, with results expressed as a percentage 
of  crude fibre relative to the original sample mass.
% Crude Fibre content = (W1-W2 (g))/(Initial Weight of  
Sample (g)) ×100
This analytical approach conforms to the standard 
principles of  fibre quantification, effectively isolating 
the acid- and alkali-insoluble dietary fibre fraction while 
accounting for mineral contamination through the ashing 
correction.

Determination of  Crude Lipid
About 3 g of  the samples (SRC, HF-10 and HF-20) were 
weighed and poured onto a dry filter paper, which was 
then rolled carefully. The rolled filter paper was placed 
into an extraction thimble, and the fat was extracted using 
a Soxhlet apparatus with ethyl ether as the solvent.
After extraction, the fat-containing solvent was transferred 
into a pre-weighed flask, and the ether was evaporated. 
To ensure complete removal of  residual solvent, the flask 
was placed in an air oven at 100°C for 30 minutes. Once 
dried, the flask was transferred to a desiccator to cool to 
room temperature. Finally, the flask was reweighed, and 
the total fat content was calculated. 
% Fat content = (weight offat/lipid obtained (gm))/
(weight of  sample (gm)) × 100

Determination of  Carbohydrate content
The carbohydrate content was calculated by difference, 
whereby the sum of  the measured proximate components 
(moisture, crude protein, crude fat, ash, and crude fibre) 



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was subtracted from 100%. This approach assumes that 
the remaining fraction primarily consists of  digestible 
carbohydrates, including sugars and starches.
%Carbohydrate content = 100 – [Moisture 
content(g/100g) + Protein content(g/100g) + Fat 
content(g/100g) + Ash content(g/100g) + Crude fibre 
content(g/100g)]

Abdominal and thoracic circumferences and of  Lee 
Obesity Index 
At the end of  the experiment, morphometric parameters 
were recorded for all obese Wistar rats. The abdominal 
circumference (AC) and thoracic circumference (TC) were 
measured using a flexible measuring tape. Additionally, 
each animal’s body length (nose-to-anus distance) and 
body weight were determined.
The Lee Obesity Index was subsequently calculated using 
the following formula:
Lee Obesity Index =(∛weight(g))/(naso-anal lenght (cm))
The abdominal/thoracic ratio (AC/TC ratio) was 
calculated as follows:
AC/TC ratio =(Abdominal Circumference (cm))/
(Thoracic Circumference (cm))

Determination of  energy intake and feed efficiency
Determination of  Energy Intake 
Energy Intake (g) = Mean food consumed X dietary 
metabolizable energy (Kcal)

Determination of  Feed Efficiency 
Feed efficiency is the ability to convert ingested food into 
body mass (Zhang et al., 2023). The weight changes of  
the animals in the SRC, HFD-10 and HF-20 groups were 
summed up weekly to the end of  the study. The weekly 
feed intakes were calculated and the feed efficiency was 
calculated as (Zhang et al., 2023).
Feed Efficiency= (weight gain (g) )/(Feed intake (g))

Carcass Analysis and Relative Organ Weight
Carcass analysis of  unshaven rats was carried out on 
the animals. After euthanasia by cervical dislocation, 
thoracotomy, and median laparotomy were performed 
on the animals to remove the organs as well as the 
adipose tissue from the retroperitoneal and epididymal 
compartments. The fat pads, which include the 
retroperitoneal fat attached to the posterior abdominal 
wall near the kidneys and inguinal fat, visceral fat 
(subcutaneous adipose tissue between the lower rib cage 
and thigh), epididymal fat located in the lower abdomen 
and connected to the epididymis will be dissected, isolated 
and weighed. The adiposity index was derived by the sum 
of  epididymal, visceral, and retroperitoneal fat weights 
and the adiposity index is expressed as a percentage.
Adiposity Index = (Total body fat (g))/(Final body weight 
(g)) × 100
The liver, kidneys, heart and brain of  the Wistar rats were 
harvested and weighed and are expressed as a percentage 
of  the body weight.

Relative organ weight = (Weight of  organ (g))/(Final 
body weight (g)) × 100

Fecal matter proximate analysis and apparent 
nutrient digestibility coefficients 
Faecal output was recorded three times per week 
throughout the experimental period. Upon completion of  
the experiment, faeces collected from individual rats were 
stored in pre-labelled plastic containers and subsequently 
pooled by the experimental group. The pooled faecal 
samples were oven-dried, homogenized, and ground to 
a fine powder for proximate analysis (crude fibre, crude 
protein and ash content). These prepared samples were 
also used to determine apparent nutrient digestibility 
coefficients by previously described methods (Ingweye, 
2015). 
Apparent digestibility coefficient = (Nutrient in feed-
Nutrient in faeces)/(Nutritient in feed) × 100

Ethical Consideration
The animals were cared for and handled in full compliance 
with the most stringent ethical guidelines established 
for the use of  animals in scientific research. The study 
protocol was approved by the Research Ethics Committee 
of  the University of  Port Harcourt with approval number 
UPH/CEREMAD/REC/MM107/054.

Statistical Analysis
The statistical analysis was performed using IBM 
Statistical Product and Service Solutions (SPSS)version 
26. The one-way ANOVA was used to determine the 
difference among the groups followed by Fisher’s Least 
significant difference. A p-value of  less than 0.05 was 
considered statistically significant (p<0.05).

RESULTS AND DISCUSSIONS
Table 1 shows the proximate composition of  the three 

Table 1: Feed Proximate Analysis 
Nutrients (g/100g) SRC HF-10 HF-20
Protein 19.38 17.64 14.22
Ash 6.75 6.54 5.61
Carbohydrate 50.24 45.72 41.69
Fibre 4.22 3.84 3.5
Moisture 15.04 14.23 13.77
Lipids 4.37 12.03 21.21

SRC= standard rat chow
HF-10= SRC+ 10% beef  tallow
HF-20= SRC+ 20% beef  tallow

rat diets; the standard rat chow (SRC), SRC supplemented 
with 10% beef  tallow (HF-10), and SRC supplemented 
with 20% beef  tallow. Our data show that the protein 
content decreased with increasing beef  tallow inclusion 
(SRC: 19.38 g/100g; HF-10: 17.64 g/, HF-20: 14.22 
g/100g). The ash content was highest in SRC (6.75 
g/100g) and declined with tallow supplementation 



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(6.54 g/100g and 5.61 g/100g for HF-10 and HF-20 
respectively. Carbohydrates followed a similar trend 
of  decreasing with increasing tallow supplementation 
(SRC: 50.24 g/100g; HF-10: 45.72 g/100g; HF-20: 41.69 
g/100g). Also, dietary fibre was highest in SRC (4.22 
g/100g) and decreased with tallow addition: 3.84 g/100g 

and 3.50 g/100g for HF-10 and HF-20 respectively. 
Expectedly, lipid content increased proportionally with 
tallow inclusion (SRC: 4.37 g/100g; HF-10: 12.03 g/100g; 
HF-20-21.21 g/100g) while moisture content marginally 
reduced with tallow inclusion; SRC: 15.04 g/100g vs. 
14.23 and 13.77 g/100g in HF-10 and HF-20 respectively. 

Table 2: Feed calorific content, percentage energy and efficiency
Calorific content and % energy SRC HF-10 HF-20
Protein calorific content (4 Kcal) 77.52 70.56 56.88
Protein energy percentage (%) 21.4 19.5 13.7
Carbohydrate (4 Kcal) 200 182.86 166.76
Carbohydrate energy percentage (%) 55.40 50.50 40.00
Fat calorific content (9 Kcal) 39.33 108.18 190.89
Fat energy percentage (%) 10.8 29.9 46.1%
Total calorific content 361.85 361.62 414.41
Total calorific content in Kcal/kg 3618.5 3616.2 4144.1
Feed Efficiency 37.63 43.82 62.00

SRC= standard rat chow
HF-10= SRC+ 10% beef  tallow
HF-20= SRC+ 20% beef  tallow

Table 3: Effect of  feed formulations on morphometric parameters of  male Wistar rats.
Parameters SRC HF-10 HF-20
Body weight (g) 242.12± 2.92 272.16±0.02a 335± 1.12a,b

Lee’s Obesity Index 0.32±0.01 0.33±0.02 0.38±0.01a,b

Abdominal circumference (AC) 15.70+0.35 15.52±0.97 22.48±0.93a,b

Thoracic circumference (TC) 15.40±0.24 16.40±0.39 16.44±0.70
AC/TC ratio 1.02±0.04 0.95±.06 0.95±.06
Absolute adipose tissue weight (g) 1.57±0.26 2.22±0.55a 13.76±1.43a,b

Adiposity Index (%) 0.65±0.11 0.82±0.20a 4.09±0.34a,b

SRC = standard rat chow; HF-10= SRC+ 10% beef  tallow; HF-20= SRC+ 20% beef  tallow
All values are expressed as Mean ± standard error of  the mean
ap < 0.05, significant change when compared with the control, 
bp < 0.05, significant change when compared with the HF-10 group

Table 2 presents the calorific content and percentage 
energy contribution of  macronutrients (protein, 
carbohydrates, and fat) across three feed types: SRC, 
HF-10, and HF-20. Total calorific content per kilogram 
ranged from 3616.2 Kcal/kg (SRC) to 4144.1 Kcal/
kg (HF-20), with HF-20 exhibiting the highest energy 
density. Protein contributed 21.4%, 19.5%, and 13.7% 
of  total energy in SRC, HF-10, and HF-20, respectively, 

showing a progressive decline. Carbohydrates were the 
primary energy source in SRC (55.4%) but decreased 
to 40% in HF-20. Conversely, fat energy contribution 
increased from 10.8% (SRC) to 46.1% (HF-20), reflecting 
a shift toward higher fat content in HF feeds. The HF-10 
and HF-20 diets showed a 16.5% and 64.8% increase in 
feed efficiency compared to the SRC diet
Table 3 compares the impact of  the various feed 

formulations (SRC (control), HF-10 (10% fat), and HF-
20 (20% fat) on key morphometric parameters in male 
Wistar rats. The results indicate that the body weight of  
animals increased significantly from 242± 2.92g as seen 
in the SRC diet group to 272±0.02g and 335± 1.12g in 
the HF-10 and HF-20 diets (p<0.05). Following this, 
Lee’s obesity index increased significantly from 0.32 in 
the SRC group to 0.38 in the HF-20 group (p<0.05), 
indicating a higher degree of  obesity. Similarly, abdominal 
circumference (AC) also significantly increased in the 
HF-20 group (22.48 cm) compared to the SRC (15.70 

cm) and HF-10 (15.52 cm) groups (p<0.05). However, 
the thoracic circumference (TC) only slightly increased 
among the high-fat diet groups compared to the SRC. 
Hence, the ratio of  abdominal to thoracic circumference 
(AC/TC) remained consistent across all groups. Absolute 
adipose tissue weight and adiposity index showed a dose-
dependent increase with dietary fat content. While the 
HF-10 group showed moderate increases in fat mass 
(2.22 g) and adiposity (0.82%), the HF-20 group showed 
a marked elevation (13.76 g and 4.09%, respectively).
Table 4 shows the impact of  dietary formulation SRC, 



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Table 4: Effect of  feed formulations on relative organ weights of  male Wistar rats
Relative organ weights (g) SRC HF-10 HF-20
Left kidney 0.28±0.02 0.40±0.03 0.41±0.07
Right kidney 0.28±0.01 0.35±0.01a 0.42±0.02a, b

Liver 0.27±.014 2.95±0.26a 3.40±0.19a

Spleen 0.27±0.01 0.28±0.02 0.21±0.02b

Heart 0.32± 0.02 0.36±0.01 0.54±0.03a, b

Pancreas 0.36±0.03 0.37±0.04 0.54±0.03a, b

Left testis 0.54±0.03 0.54±0.01 0.45±0.01a, b

Right testis 0.57±0.04 0.54±0.01 0.47±0.02a

SRC = standard rat chow; HF-10= SRC+ 10% beef  tallow; HF-20= SRC+ 20% beef  tallow
All values are expressed as Mean ± standard error of  the mean
ap < 0.05, significant change when compared with the control, 
bp < 0.05, significant change when compared with the HF-10 group

Table 5: The faecal proximate composition analysis 
Nutrients (%) SRC HF-10 HF-20
Crude Protein 20.49 19.7 19.86
Ash 18.93 21.36 20.44
Carbohydrate 29.42 28.35 28.53
Fibre 15.35 14.79 14.89
Moisture 13.28 12.6 13.03
Crude Fat 2.53 3.2 3.25

SRC= standard rat chow
HF-10= SRC+ 10% beef  tallow
HF-20= SRC+ 20% beef  tallow

Table 6: The apparent nutrient digestibility coefficients 
of  various feed formulations in male Wistar rats.
Nutrient
Digestibility 

SRC HF-10 HF-20

% Fat digestibility 42.1 73.34 84.67
% Protein -5.73 -7.70 39.66
% Carbohydrate 41.44 37.99 31.57

SRC= standard rat chow
HF-10= SRC+ 10% beef  tallow
HF-20= SRC+ 20% beef  tallow

HF-10 and HF-20 on the relative organ weights of  male 
Wistar rats. The results revealed significant alterations 
in multiple organs, demonstrating a dose-dependent 
relationship with dietary fat content. Both kidneys 
exhibited increased weights in high-fat groups compared 
to SRC, with the right weighing heavier in the HF-10 
(0.35 ± 0.01 g) and HF-20 (0.42 ± 0.02 g) compared 
to the control, p < 0.05). Similarly, the liver underwent 
apparent hypertrophy in fat-fat groups as shown as their 
relative weight increased from 0.27 ± 0.01 g (SRC) to 2.95 
± 0.26 g (HF-10) and 3.40 ± 0.19 g (HF-20) (p < 0.05). 
However, the spleen showed a reduced weight in the HF-
20 group (0.21 ± 0.02 g) compared to SRC (0.27 ± 0.01 g) 
and HF-10 (0.28 ± 0.02 g) (p < 0.05). The heart and the 
pancreas increased significantly in HF-20 (heart: 0.54 ± 
0.03 g; pancreas: 0.54 ± 0.03 g) vs SRC (heart: 0.32 ± 0.02 
g; pancreas: 0.36 ± 0.03 g) and HF-10 (p < 0.05) while 
testicular weights declined in the HF-20 group (left: 0.45 
± 0.01 g; right: 0.47 ± 0.02 g) relative to SRC (left: 0.54 ± 
0.03 g; right: 0.57 ± 0.04 g) (p < 0.05).
The faecal proximate composition analysis revealed 

distinct patterns in nutrient excretion across the three 
dietary groups (SRC, HF-10, and HF-20) as shown in 
Table 5. Crude protein content showed minimal variation 
between diets (19.7-20.5%), suggesting consistent 
protein metabolism regardless of  dietary fat content. 

There was a slight increase in ash excretion in the high-
fat groups (21.4% in HF-10, 20.4% in HF-20) compared 
to the control (18.9%). Carbohydrate and fibre fractions 
demonstrated remarkable stability across all diets, with 
values around 28-29% for carbohydrates and 14-15% 
for fibre. Moisture content showed a modest reduction 
in high-fat groups (12.6-13.0%) compared to the control 
(13.3%).
Table 6 shows the apparent nutrient digestibility 

coefficients in macronutrient utilization across the 
experimental diets. Fat digestibility exhibited a pronounced 
dose-dependent increase, rising from 42.1% in the SRC 
group to 73.3% in HF-10 and further to 84.7% in HF-20, 
demonstrating enhanced lipid absorption efficiency with 
higher dietary fat content. 
Protein digestibility showed negative digestibility 
coefficients in both SRC (-5.7%) and HF-10 (-7.7%) 
groups while the HF-20 diet showed a remarkable reversal 
to positive protein digestibility (39.7%). Carbohydrate 
digestibility displayed an inverse relationship with dietary 
fat content, gradually declining from 41.4% in SRC to 
38.0% in HF-10 and 31.6% in HF-20. 

Discussion 
Obesity and its associated metabolic disorders have 
become major public health concerns worldwide, 
with high-fat diets (HFDs) widely implicated in their 
development (Duan et al., 2018; Tang et al., 2024). High-



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fat diets (HFDs) are employed in experimental settings to 
induce obesity, with formulations typically deriving 40–
60% of  total caloric intake from lipids (An et al., 2022; Wali 
et al., 2020). This approach reinforces the well-established 
paradigm that obesity development is fundamentally 
driven by chronic positive energy balance. To address 
the dual challenges of  nutritional inconsistencies in 
non-commercial high-fat diet formulations and limited 
accessibility of  prepackaged diets, the study developed 
standardized HFDs using regionally available beef  tallows 
as a cost-effective fat source. The present investigation 
systematically evaluated both the nutritional profile of  
these formulated diets and their efficacy in promoting 
obesity progression using male Wistar rat models.
Proximate analysis of  the diets in the present study 
revealed that increasing beef  tallow supplementation 
from 10 to 20% reduced the protein content from 
19.38 to 14.22 g/100g, carbohydrates from 50.24 to 
41.69 g/100g and fibre from 4.22 to 3.50 g/100g) while 
increasing the lipid content from 4.37 to 21.21 g/100g 
(Table 1). The reduction in carbohydrate content is 
consistent with findings from a previous study that 
reported that HFDs typically displace carbohydrates to 
elevate energy density (Hariri & Thibault, 2010). The HF-
20 diet exhibited the highest energy content (4144.1 kcal/
kg), with fat contributing 46.1% of  total energy, which 
is consistent with diet-induced obesity models (Hariri & 
Thibault, 2010; Winzell & Ahrén, 2004). The dramatic 
shift in the energy contribution from fat is a key feature 
of  an obesogenic diet, which promotes the accumulation 
of  fat stores while potentially impairing glucose and lipid 
metabolism (Grabner et al., 2021; Richard et al., 2020).
However, the decline in protein-derived energy from 
21.4% in SRC to 13.7% in the HF-20 diet contrasts with 
some commercial HFDs where protein levels are often 
stabilized to prevent malnutrition (Levin et al., 1997). 
HFDs, particularly those in saturated fats suppress protein 
metabolism in favour of  lipid utilization (Yiannakou et 
al., 2023). Feed efficiency measures the ability of  the 
animal to convert ingested food into body mass (Benoit 
& Mottet, 2023). The 64.8% higher feed efficiency in HF-
20 mirrors predictive models linking energy density to 
calorie intake efficiency in rats (Beheshti et al., 2018) and 
suggests that high-fat diets support the promote obesity 
and lipogenesis and promote fat storage, due to the 
higher caloric density provided by the fat by lipogenesis 
and, even when food intake is not significantly increased 
(Jahan et al., 2024; Strable & Ntambi, 2010; Zhang et al., 
2023). 
The present study demonstrated significant dose-
dependent increases in body weight and adiposity markers 
in male Wistar rats fed beef  tallow-supplemented high-fat 
diets (HFDs). 
The progressive increase in body weight from 242 ± 2.92 
g (SRC) to 335 ± 1.12 g (HF-20) (p<0.05) corresponds 
with previous reports of  HFD-induced weight gain in 
rodent models (Levin et al., 1997), however, the magnitude 
of  increase (38% in HF-20 vs SRC) exceeds the 20-

30% typically reported for 60% fat diets (Buettner et al., 
2007) but falls with the 35% weight increase for obesity 
classification reported in our facility (Alor & Chinko, 
2022). This suggests that have potent obesogenic effects. 
The elevated Lee’s index (0.38 in HF-20) confirms the 
development of  true obesity, not merely increased lean 
mass, matching the standard criteria (Hariri & Thibault, 
2010). The larger increase in abdominal circumference 
(43% in HF-20 vs SRC) when compared to the change in 
thoracic circumference (6.7% in HF-20 vs SRC) indicates 
preferential visceral fat deposition. This aligns with clinical 
observations of  classic abdominal obesity in metabolic 
syndrome (Choi et al., 2015; Després & Lemieux, 2006). 
The stable AC/TC ratio across groups suggests this 
regional fat partitioning occurred proportionally at all 
diet levels. Visceral obesity, as indicated by an elevated 
AC/TC ratio, is a well-known risk factor for metabolic 
diseases, including insulin resistance, fatty liver disease, 
and cardiovascular conditions (Agboola et al., 2023). 
This highlights the detrimental effects of  high-fat diets 
on fat distribution and underscores the importance of  
abdominal fat as a marker for obesity-related metabolic 
diseases (Després, 2012; Ritchie & Connell, 2007). The 
substantial increase ( 8.8 fold) in absolute adipose tissue 
weight in high-fat diets (13.76 g in HF-20 vs 1.57 g in 
SRC) exceeds the 5-6-fold changes previously reported 
with 45-60% fat diets (Softic et al., 2017). The adiposity 
index (4.09% in HF-20 vs 0.65 in SRC) reached levels 
comparable to genetically obese Zucker rats (She et 
al., 2013; Sisk et al., 2001). This suggests that beef  
tallow promotes particularly efficient fat storage due 
to increased caloric intake as observed in this study 
(Table 1). This contrasts with plant-oil-based HFD 
showing lower adiposity indices (2.5-3.5%) at similar fat 
percentages (Cintra et al., 2012). Organ weight alterations 
were particularly striking with an increase observed in 
the weight of  the liver and the kidney and a reduction 
in the weight of  the spleen and testes among the HF-
10 and HF-20 diet groups compared to the control SRC 
group (Table 4). The apparent hepatic hypertrophy (from 
0.27 g in SRC to 3.40 g in HF-20) aligns with studies 
showing lipid accumulation in HFD-fed rats (Softic 
et al., 2017), while renal enlargement may reflect early 
metabolic stress (Declèves et al., 2011). The apparent 
spleen atrophy in HF-20 (0.21 g vs. 0.27 g in SRC) aligns 
with a previous study that observed a reduction in spleen 
weight in mice chronically fed with HFD (Strandberg et 
al., 2009), however, this conflicts with reports of  HFD-
induced splenomegaly in obese female rats fed with HFD 
(Altunkaynak et al., 2007) suggesting fat-source-specific 
immune modulation. Testicular weight reduction (0.54 g 
in SRC to 0.45 g in HF-20) supports evidence of  HFD-
induced reproductive dysfunction (Aly & Polotsky, 2017; 
Bakos et al., 2011).
Faecal proximate analysis revealed stable protein (19.7–
20.5%), carbohydrate (28–29%) and fibre (14–15%) and 
water (13.28% in SRC vs 12.6 and 13.03% in HF groups) 
excretions across diets. There was a marginal increase in 



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Am. J. Food. Sci. Technol. 4(2) 34-43, 2025

ash ((18.9 - 21.4%) and fat (2.53 to 3.25%) in HF groups 
compared to the control. The rise in fat excretion was 
lower than expected given the dietary fat load, suggesting 
enhanced lipid absorption efficiency. The observed faecal 
fat excretion reflects a saturation of  intestinal absorption. 
These findings demonstrate that while high dietary fat 
intake led to modest increases in faecal fat excretion, the 
majority of  absorbed lipids are efficiently partitioned 
into adipose tissue storage leading to disproportionate 
gains in adiposity despite marginal lipid excretion. The 
preferential visceral/abdominal fat accumulation suggests 
adipose tissue acts as a primary lipid dump, particularly 
for saturated fats. These observations align with the 
“spillover” hypothesis of  lipid metabolism, where 
adipose tissue buffers excess lipid influx, explaining how 
even marginally reduced absorption efficiency can coexist 
with significant obesity development (Ravussin & Smith, 
2002; Sakers et al., 2022). 
A progressive increase in fat digestibility was observed 
with rising fat content, which can be attributed to 
increased bile acid secretion stimulated by fat leading to 
an enhanced activity of  pancreatic lipase and improved 
micelle formation in the intestine, which facilitate efficient 
fat emulsification and absorption in high-fat diets (Wang 
et al., 2025). The apparent negative protein digestibility, 
especially in the 20% HFD group may indicate 
inefficient nitrogen utilization, possibly due to metabolic 
disturbances induced by chronic high-fat intake such as 
low-grade inflammation, gut microbiota dysbiosis, and 
increased oxidative stress, which may impair amino acid 
absorption and increase protein turnover (Wang et al., 
2025). Additionally, high-fat diets have been shown to 
downregulate intestinal amino acid transporters, further 
reducing protein digestibility (Hijo et al., 2019). The 
decline in carbohydrate digestibility as seen in a study may 
be due to the metabolic shift from glucose oxidation to 
greater reliance on lipid metabolism (Ludwig et al., 2021). 
This metabolic adaptation is well-documented in high-
fat experimental models, where insulin resistance and 
reduced expression of  carbohydrate transporters (e.g., 
SGLT1, GLUT2) impair glucose uptake and utilization 
(Hijo et al., 2019; Ludwig et al., 2021). 

CONCLUSION
Evidence from the present study shows that a high-fat 
diet containing 20% beef  tallow (HF-20) effectively 
induced obesity and associated metabolic disturbances 
in male Wistar rats. The findings demonstrate a clear 
dose-response relationship between dietary fat content 
and the development of  obesity-related phenotypes. 
The HF-20 increased body weight, feed efficiency, 
nutrient digestibility and visceral fat accumulation. These 
findings highlight the use of  HFD in understanding 
the pathophysiology of  obesity and metabolic disease, 
while also providing a practical animal obesity model for 
preclinical research.

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