Apologies for the period of dormancy. I’m back and I’m bringing you new articles every Wednesday. With that said, here we go.
Introduction: Men and women store fat on different areas of the body. Women store fat in larger amounts of subcutaneous adipose tissue (the fat under the skin) and men store more visceral fat (the fat around the organs). In general, women have more body fat than men. How much adipose tissue contributes to whole body metabolism is not well known; therefore, this was the aim of the study.
Methods: This was a large cohort coming from hundreds of men and women. The researchers looked at adipose tissue gene expression as well as expression of genes involved in mitochondrial function.
- For the two sexes, fat mass and fat free mass positively correlated with resting metabolic rate (when one went up, the other went up).
- Women have a higher metabolic rate per kilogram adipose tissue than men.
- Women have a higher expression of genes related to mitochondrial function than men.
- Women have a higher number of brown adipocytes in subcutaneous adipose tissue than men.
Discussion: Just to give you an idea of the relative contributions of tissue to basal metabolic rate (BMR), the brain and internal organs account for 70-80% but only make up 5% of the body weight. Skeletal muscle, which everyone in your gym says influences BMR the most, is 20 times lower than the internal organs. Skeletal muscle accounts for about 15% of a person’s BMR. Adipose tissue falls in at around 6% of BMR so we can say it is not that active of a tissue.
From the lab to the gym: So what’s the main takeaway of this study? The practical message is from bullet point 4 of the results and particularly a molecule found in those brown adipocytes known as UCP1. UCP1 is a protein that allows the mitochondria to create heat in the brown adipocytes. Women have a higher amount of UCP1 in their subcutaneous adipose tissue (the fat you want to lose under your skin). Therefore, this study suggests that women have a higher capacity to burn calories by converting energy to heat. Of course the internal organs and muscle are going to contribute the most to your BMR, but the higher metabolic rate of adipose tissue in women gives them an advantage to burn more calories in a resting state than men.
Nookaew et al J Clin Endocrinol Metab. 2013 Feb;98(2):E370-8.