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.

 

Caloric restriction - even better with exercise

In Dr. Fuhrman’s book Eat to Live, he draws attention to studies suggesting that restricting number of calories consumed while maintaining adequate nutrition extends lifespan. Although human research on the subject of caloric restriction (CR) is still in its early stages, studies on a number of different species have shown that metabolic rate slows, body temperature decreases, and lifespan is dramatically elongated when calories are restricted. In experimental animals, long-term CR with adequate nutrition is the most effective means to slow aging and prolong lifespan.1 Humans practicing caloric restriction (CR) tend to have low body fat, low levels of chronic inflammation, low blood pressure, and low levels of cardiovascular disease risk factors.2

We know that exercise benefits the cardiovascular system and reduces the risk of cardiovascular disease. Regular aerobic exercise increases the heart’s pumping efficiency, reduces resting heart rate and blood pressure, decreases total and LDL cholesterol, decreases triglycerides, and reduces stress.3,4

An interesting new study posed this question:

For overweight individuals, which produces greater cardiovascular benefit: weight loss via restricting a certain amount of calories from the diet or weight loss via restricting a half of those calories from the diet and burning the other half via exercise?

Running

As part of a larger human study on CR and longevity, 36 overweight participants were assigned to one of three groups for a period of six months: a control group who ate a weight-maintaining quantity of calories, a group who restricted calories by 25% (CR), or a group who restricted calories by 12.5% and burned another 12.5% via exercise (CR+EX).

After six months, weight loss, total fat loss, visceral fat loss, and systolic blood pressure (top number) reduction were similar between the CR and CR+EX groups. However, only the CR+EX group showed significant improvements in diastolic blood pressure (bottom number), LDL cholesterol, and insulin sensitivity.5

Achieving a healthy weight by restricting calories is beneficial, but this is only one component of a disease-preventing lifestyle. This study demonstrates that exercise provides cardiovascular benefit above and beyond calorie restriction alone for individuals attempting to lose weight. According to these results, those practicing calorie restriction with the intention of achieving enhanced longevity can expect to reap additional benefits from exercise.

Dr. Fuhrman’s diet-style effectively and naturally reduces calories by providing a high volume of high nutrient low calorie foods, providing phytochemical benefit along with a smaller number of calories. For achieving excellent health, exercise is an essential addition to this healthy eating style.

 

References:

1. Fontana L. The scientific basis of caloric restriction leading to longer life. Curr Opin Gastroenterol. 2009 Mar;25(2):144-50.

2. Holloszy JO, Fontana L. Caloric restriction in humans. Exp Gerontol. 2007 Aug;42(8):709-12. Epub 2007 Mar 31.

Fontana L, Villareal DT, Weiss EP, et al. Calorie restriction or exercise: effects on coronary heart disease risk factors. A randomized, controlled trial. Am J Physiol Endocrinol Metab. 2007 Jul;293(1):E197-202.

3. Sasaki JE, dos Santos MG. The role of aerobic exercise on endothelial function and on cardiovascular risk factors. Arq Bras Cardiol. 2006 Nov;87(5):e226-31.

4. Wagenmakers AJ, van Riel NA, Frenneaux MP, Stewart PM. Integration of themetabolic and cardiovascular effects of exercise. Essays Biochem.2006;42:193-210.

5. Larson-Meyer DE, Redman L, Heilbronn LK, et al. Caloric restriction with or without exercise: the fitness versus fatness debate. Med Sci Sports Exerc. 2010 Jan;42(1):152-9.