Effects of Diet on the Metabolism in Mice

¶ … Diet on the Metabolism in Mice

Metabolism is enzyme-controlled reactions that allow organisms to grow and reproduce, maintain their structures, and respond to their environments. In addition, metabolism implies all chemical reactions occurring in living organisms, such as digestion and transportation of substances between cells. Metabolism is classified into two; catabolism which is the breakdown of organic matter and anabolism which entails using energy to build cell components such as proteins and nucleic acids (Michie & Lowe, 2006). Metabolism is dependent on enzymes since enzymes catalyze metabolic reactions and allow the regulation of metabolic pathways in response to changes in the cell's environment. In addition, the metabolism of an organism determines which substances it will find nutritious and which it will find poisonous. Moreover, metabolic rate influences how much food an organism will require, and also affects how it is able to obtain that food (Roach, 2002). Just like humans, mice have been found to have a higher or lower metabolism rate depending on the food given to them. Therefore, this study used sixteen rats in the experiment to prove three hypotheses. The first study hypothesis is the effect of diet on the rate of metabolism of the mice; the second hypothesis being the impact of metabolism on weight gain among the mice and lastly, the relationship between respiration at room temperature and high-fat diet among mice. It has been confirmed in different researches that a high-fat diet has the effect of increasing metabolism rates among animals as well as weight gain. Therefore, this study aimed at confirming the accuracy of these hypotheses by conducting this laboratory test using mice fed on a high-fat and normal diets (West., et al., 1992).

Methods and Procedures

Sixteen female mice were purchased from The Jackson Laboratory (Bar Harbor, ME) and maintained in a temperature-controlled room (22°C) on a 12-h light-dark cycle. One week after arrival, the mice were divided into two groups with one group being fed on a high-fat diet while the other receiving a continuous feeding of a normal diet for six weeks. On caloric basis, the high-fat diet consisted of 58% fat from lard, 25.6% carbohydrate, and 16.4% protein, a total of 23.4 kJ/g; whereas the normal diet contained 11.4% fat, 62.8% carbohydrate, and 25.8% protein, a total of 12.6 kJ/g. Food intake and body weight were measured once a week, and blood samples were taken at indicated time points from the intraorbital retrobulbar plexus from non-fasted anesthetized mice. On the same note, ten mice were fasted overnight (1700 to 0800) and were subsequently injected with glucose (2 g/kg body wt ip).

Thereafter, tail blood was collected at 0, 15, 30, 60, and 120 min and besides, blood glucose concentrations were measured using a glucometer. All results were expressed as means ± SE. Metabolic efficiency was calculated as the energy intake divided by the body weight gain over a certain period of time. In addition, early insulin response was estimated as the increase in plasma insulin at 15 min above basal, and the KG as the glucose elimination rate between minute 15 and 60. Linear relationships were estimated using Pearson's moment correlation coefficient. Statistical comparisons were performed with Student's unpaired and paired t tests; when multiple comparisons were performed, ANOVA was used.

Results

A week after introduction of high-fat diet, body weight increased significantly more in the high-fat diet -- fed mice (+1.6 ± 0.1 g) than in the normal diet -- fed mice (+0.2 ± 0.1 g). The weight gain continued thereafter to be progressively higher in high-fat -- fed mice. The growth rate in normal diet-fed mice during the first 12 weeks was 0.40 ± 0.03 g/week which increased to 0.68 ± 0.04 g/week in high-fat diet-fed mice. The growth rate during the second phase; from week 3 onwards, was 0.10 ± 0.01 g/week in normal diet -- fed mice compared to 0.18 ± 0.03 g/week in high-fat diet -- fed mice representing an augmented growth rate of 80%.

Additionally, the energy intake was increased in high-fat diet -- fed mice compared with normal diet -- fed mice throughout the study period. With time, energy intake declined linearly, with, however, the difference between the two groups being stable. Metabolic efficiency was calculated for the initial 3-week study period, when weight gain was high but this was significantly reduced in high-fat diet -- fed mice.

Finally, respiration at room temperature among the high-fat fed mice increased gradually compared to the normal diet-fed mice. With increased body weight and energy intake, the high-fat diet fed mice after the first week had higher respiration. This was due to higher dietary intake in combination with lower metabolic efficiency.

Discussion

Several studies hypothesize that dieting subjects eating high-fat diets tend to lose more weight more rapidly than subjects eating low-fat diets leading to speculations that high-fat diets enhance weight loss by attenuating the decrease in energy expenditure typically seen with dieting (Almind & Kahn, 2004). However, such an effect has not been demonstrated in either humans or rodents. In this study we examined the effects that diet composition can have on metabolism and found that diets high in fat do in fact lead to weight loss by increasing energy expenditure.