Metabolic rate: the slower, the better

“Metabolism” has become quite a buzzword in our culture. Weight gain or inability to lose weight is often blamed on having a slow metabolism and the prevailing myth is that a faster metabolism is preferable, because it would lead to weight loss. However, having a fast metabolism does not mean that you are healthier – in fact, it may cause you to age more quickly. Many supplements claim to increase your metabolism and promote weight loss, but these are merely stimulants. Instead of trying to increase your metabolism with the goal of losing weight, I say, get your body to run on fewer calories and slow your metabolism for a longer, healthier life.

Turtle

A new study on thyroid function and longevity in families supports my view. This research is part of the Leiden Longevity Study in the Netherlands, in which recruited families had at least two siblings were alive and had reached age 90 or older – these individuals are referred to as “nonagenarian siblings”.

Since thyroid function is influenced by genetics, and thyroid hormone regulates both basal metabolic rate (energy expenditure at rest with an inactive digestive system) and overall daily energy expenditure [1], the researchers studied thyroid function and longevity in nonagenarian siblings and their family members. [2, 3]

In a study published earlier this year, it was established that middle-aged children of nonagenarian siblings had altered thyroid function compared to a control group. They tended to have higher levels of thyrotropin and lower levels of thyroxine (T4) and free triiodothyronine (free T3 – active form of the hormone), indicating lower thyroid function and therefore lower metabolic rate.[2]

A second study measured thyroid hormone levels in nonagenarian siblings and correlations to longevity of their parents. Low thyroid activity in nonagenarian siblings was indeed associated with their parents’ lifespans.[3] The average lifespan of the parents of nonagenarian siblings was an impressive 93 years.

These studies suggest that hereditary factors associated with metabolic rate (thyroid function) are associated with lifespan. This means that taking steps to slow metabolic rate, rather than accelerate it, could be beneficial.

How might a higher metabolic rate promote aging?

One theory is that increased energy expenditure shortens lifespan – that the human body works somewhat like a machine – if it is forced to work too hard and too fast, it will “wear out” more quickly. In a number of small mammal species, daily energy expenditure is indeed inversely related to lifespan, supporting this theory.[4] Accordingly, caloric restriction has been consistently shown to prolong maximal lifespan up to 60% in a variety of species.[5] By reducing calorie intake and still meeting micronutrient demands, daily energy demands are also reduced. Eating predominantly high nutrient, low calorie foods can help to achieve this effect – the body’s micronutrient requirements are satisfied with fewer calories, leading to reduced energy intake and therefore reduced energy demand.

Oxidative damage resulting from the continuous production of reactive oxygen species (as a byproduct of energy metabolism) over time is a related theory of aging.[6] A high nutrient diet would also be effective in this case, since whole plant foods provide both variety and abundance of antioxidants.

The point is we want to eat a diet with excellent micronutrient quality, we will not be hungry as often, we will be comfortable with eating less, and our metabolic rate will slow so that we can eat less and not get too thin.

Don’t buy into the myth – when it comes to metabolism, faster is not better.

 

Image credit: Flickr - Zevotron

References:

1. Kim, B., Thyroid hormone as a determinant of energy expenditure and the basal metabolic rate. Thyroid, 2008. 18(2): p. 141-4.
2. Rozing, M.P., et al., Low serum free triiodothyronine levels mark familial longevity: the Leiden Longevity Study. J Gerontol A Biol Sci Med Sci, 2010. 65(4): p. 365-8.
3. Rozing, M.P., et al., Familial Longevity Is Associated with Decreased Thyroid Function. J Clin Endocrinol Metab, 2010.
4. Speakman, J.R., et al., Living fast, dying when? The link between aging and energetics. J Nutr, 2002. 132(6 Suppl 2): p. 1583S-97S.
5. Fontana, L., The scientific basis of caloric restriction leading to longer life. Curr Opin Gastroenterol, 2009. 25(2): p. 144-50.
6. Hulbert, A.J., et al., Life and death: metabolic rate, membrane composition, and life span of animals. Physiol Rev, 2007. 87(4): p. 1175-213.