Metabolic Response to Over and Underfeeding May Predispose to Obesity

sharma-obesity-balanceChanges in caloric balance are long known to affect metabolic requirements – in general, overfeeding tends to  increase metabolic rate, whereas underfeeding (or fasting) tends to lower metabolic rate. However, the magnitude of these changes tend to vary substantially between individuals.

Now a study by Martin Reinhardt and colleagues, published in the International Journal of Obesity, shows that this variation in response to overfeeding and fasting may predispose some individuals to obesity (thrifty phenotype).

The study was conducted in 77 individuals (58 men and 19 women, average age 36, average BMI 26) while housed in a clinical research unit and included measurement of  24-hour energy expenditure (EE) using a whole-room indirect calorimeter (the gold-standard for such measurements). Measuring also included 24-hour core body temperature during 24h each of fasting and 200% overfeeding with a diet consisting of 50% carbohydrates, 20% protein and 30% fat. Body composition was measured by dual X-ray absorptiometry.

Firstly, the researchers found that a greater %EE decrease with fasting correlated with a smaller %EE increase with overfeeding, or in other words, individuals who responded with a greater decrease in caloric expenditure in response to fasting also showed a lower increase in caloric expenditure with overfeeding.

The %EE decrease with fasting was associated with both fat mass and abdominal fat mass as well as a lower 24-hour core body temperature  (even after accounting for a number of covariates). A 0.1°C lower core body temperature was associated with a 1.4% greater decrease in EE during fasting.

From these findings the authors conclude that,

“body temperature may be a further defining feature of the human thrifty phenotype and offer insight into contributors to the inter-individual variation observed in energy expenditure responses to caloric restriction or excess.”

They also suggest that perhaps careful measurements of body core temperature could be harnessed to direct weight loss or weight maintenance efforts during life style interventions.

If nothing else, the study nicely documents that we are not all equal when it comes to how our bodies respond to over or underfeeding.

Edmonton, AB

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