Metabolism May Not Slow After 20 – So Why Do We Still Gain Weight? By Janet Cade, University of Leeds for Natural Blaze
For a long time, it was believed that after the age of 20 your metabolism decreased dramatically – making it harder to lose weight and keep in shape. But a recent study has shown our metabolism – also known as energy expenditure – stays relatively stable between the ages of 20 and 60, before decreasing at older ages.
The researchers looked at existing studies on energy expenditure from 29 different countries. In total, they looked at data on around 6,400 people from birth to 95 years of age. Each study measured energy expenditure using a method called doubly labelled water. This has participants drink a special type of water, in which a safe, radioactive marker has been added. The marker identifies the hydrogen and oxygen present in the water, which allows researchers to track how quickly the body processes both. Urine samples are then taken from each person to track the rate they’ve both travelled through the body. This gives researchers an accurate measure of a person’s metabolic rate – the amount of energy they used in a day.
The analysis showed that energy expenditure (metabolism) rapidly increased from birth to one year. After this, energy expenditure gradually decreased until the age of 20, at which point it became stable until age 60 – even during pregnancy. After 60 was when energy expenditure begins to fall. These findings were true even when researchers took into account different factors – such as physical activity and body composition (how much fat or muscle a person had and how much they weighed) – which can affect a person’s metabolism.
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This study builds on our understanding of the human metabolism. Knowing how our metabolism may (or may not) change during our lives can be important for knowing how diseases – such as obesity, diabetes, heart disease and even some cancers – can be treated.
But one problem with the study’s findings is that they didn’t take into account a person’s energy intake. Many people still see their weight increase as they get older, despite their metabolism staying relatively the same throughout their life. This suggests that weight gain isn’t a result of a slowing metabolism. Rather, it’s more likely to be due to eating more food (energy) than our body uses.
