The Metabolic War

Author :Akshita Arora INFS Faculty

Key points:

  • Women have lower Basal Metabolic Rate (BMR), Resting Metabolic Rate (RMR), Total Daily Energy Expenditure (TDEE) and basal fat oxidation as compared to the men.
  • Metabolic adaptation is quicker in women as compared to the men.
  • Substrate utilization varies with the different phases of the menstrual cycle in women.
  • Women have greater type I muscle fibers and therefore greaterintramuscular triglycerides (IMTG) content than men. Thus, they, tend to use more fatty acids as a fuel during the exercise.

Keywords: Metabolism, nutrition, training, gender, women

Introduction

As per National Family Health Survey (NHFS), the obesity rate in Indian females is 133% higher than males. Also, one commonly observed trend amongst couples who are trying to get fit is that the female tends to lose lesser weight overall as compared to the male even after doing everything right, putting in more efforts and following her diet and training more diligently. So there seem to be gender-based differences in the metabolism which affect this relative rate of fat loss, fat gain and other aspects of nutrition. In this article, we aim to highlight how metabolism differs between the two genders and its implication on the diet and training.

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The different metabolisms:

  1. Energy metabolism during the non-exercise period:

Several studies have shown that women have much lesser Resting metabolic rate (RMR), Basal Metabolic Rate (BMR) and 24 Hours Energy Expenditure even for the matched weight and level of the physical activity [1]. This difference is likely due to the differences in their body compositions , where women have higher essential body fat resulting in  comparatively lesser lean body mass (LBM) [2,3]. Despite having higher body fat, evidence shows that women have comparatively lower basal fat oxidation rate [4].This partially explains why there are more obese women than men .  

Also, this has a direct relationship to the rate of fat loss. A woman will lose lesser weight as compared to a man even when they are on the same percentage of caloric deficit. Thus, it’s commonly observed that to lose more fat, women tend to diet harder by aggressively cutting the calories and spending hours on the treadmill daily but after some time, even that approach doesn’t seem to work. This is because a woman adapts to calorie restriction much quicker than a man. Thus, a quicker adaptation of metabolism means women will reach their plateau sooner than men [5]. Adding to that, substrate utilisation in women also changes with different phases of the menstrual cycle. The body uses more glucose for energy during follicular phase while fat oxidation rate increase during the luteal phase [6,7]. Several studies have also indicated that changing the macronutrient ratio of the diet in accordance with these phases can be helpful in improving the rate fat-loss or increasing the strength in women.

2.Energy metabolism during the exercise period:

Exercise period is a time where women hold an advantageous position. They tend to use more fatty acids for fuel while exercising, due to higher intramuscular triglycerides (IMTG) content and utilization [8-10]. This happens because Type I muscle fibers are predominant in women which uses IMTG as a primary fuel. Estrogen might also be an influencing aspect here. This means that even though women will burn lesser calories than men for an equal exercise volume and intensity, most of those calories will come by oxidizing fats. Increased fat oxidation rate implies women utilize lesser proportion of energy from proteins and carbohydrates.

Now, this is also very important with sports nutrition perspective. Lesser reliance on carbohydrates means women utilise lesser glycogen for energy and therefore they don’t need much carbohydrates post workout for replenishing glycogen. Also, lesser protein oxidation means women can preserve their lean muscle mass better than men due to the reduced rate of muscle protein breakdown.
Conclusion

It is now evident that women can’t be considered as just a scaled-down version of men. There are several gender-based differences in the physiology, body compositions, fat storage patterns, energy metabolism etc. that primarily arises due to the difference in the sex hormones. Also, women havea menstrual cycle which influences these sex hormones and alter their relative levels on the monthly basis and further complicate the women’s physiology and metabolism.Thus, a dietary strategy that works well for men may not be the most appropriate or even prove impossible for women and thus, women are a special population with distinct nutrition and training requirements
References:

  1. Ferraro, R., Lillioja, S., Fontvieille, A. M., Rising, R., Bogardus, C., &Ravussin, E. (1992). The lower sedentary metabolic rate in women compared with men. The Journal of clinical investigation90(3), 780-784.
  2. Cunningham, J. J. (1980). A reanalysis of the factors influencing basal metabolic rate in normal adults. The American journal of clinical nutrition33(11), 2372-2374.
  3. Janssen, I., Heymsfield, S. B., Wang, Z., & Ross, R. (2000). Skeletal muscle mass and distribution in 468 men and women aged 18–88 yr. Journal of applied physiology89(1), 81-88.
  4. Blaak, E. (2001). Gender differences in fat metabolism. Current Opinion in Clinical Nutrition & Metabolic Care4(6), 499-502.
  5. Valle, A., Catala-Niell, A., Colom, B., Garcia-Palmer, F. J., Oliver, J., & Roca, P. (2005). Sex-related differences in energy balance in response to caloric restriction. American Journal of Physiology-Endocrinology and Metabolism289(1), E15-E22.
  6. Devries, M. C., Hamadeh, M. J., Phillips, S. M., &Tarnopolsky, M. A. (2006). Menstrual cycle phase and sex influence muscle glycogen utilization and glucose turnover during moderate-intensity endurance exercise. American Journal of Physiology-Regulatory, Integrative and Comparative Physiology291(4), R1120-R1128.
  7. Ashley, C. D., Bishop, P., Smith, J. F., Reneau, P., & Perkins, C. (2000). Menstrual Phase Effects on Fat and Carbohydrate Oxidation During Prolonged Exercise in Active Females. Journal of Exercise Physiology Online3(4).
  8. Tarnopolsky, M. A. (2008). Sex differences in exercise metabolism and the role of 17-beta-estradiol. Medicine and Science in Sports and Exercise40(4), 648-654.
  9. Horton, T. J., Pagliassotti, M. J., Hobbs, K., & Hill, J. O. (1998). Fuel metabolism in men and women during and after long-duration exercise. Journal of Applied Physiology85(5), 1823-1832.
  10. Steffensen, C. H., Roepstorff, C., Madsen, M., &Kiens, B. (2002). Myocellular triacylglycerol breakdown in females but not in males during exercise. American Journal of Physiology-Endocrinology and Metabolism282(3), E634-E642.

 

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