Science of Sport: Thermogenesis - It’s not just what you eat…

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…but how and when you eat it, according to new UK research. For most athletes, maintaining optimum weight is vital to performance, especially as excess weight in the form of fat is an instant recipe for slower times. Although maintaining a daily calorie balance (calories consumed equal to calories expended) plays a major role in weight maintenance, other mechanisms are also important, including thermogenesis, whereby small amounts of excess calories are burned off as heat, rather than stored as fat.

Thermogenesis is thought to explain why, for example, an athlete in hard training, burning anything up to 6,000kcals per day, who consumes an extra 100kcals per day (the amount contained in a banana) beyond his or her daily calorie expenditure figure, doesn’t gain the extra weight that the simple calorie balance theory would predict!

Now researchers in Nottingham studying the thermic effect of food (whereby the digestion, absorption and metabolism of food acts to raise metabolic rate and calorie expenditure) have discovered that the regularity of meals affects the rate of thermogenesis and subsequent calorie ‘burn’⁽¹⁾

Nine healthy lean women were asked to continue consuming their normal diet for 14 days in one of two patterns:

• Taken as six small meals per day, eaten at regular intervals (A);
• Taken as three to nine meals per day, eaten at irregular intervals and varied at random throughout the 14-day period (B).

After 14 days, all the women resumed their usual eating patterns for two weeks, then switched to the other group for a further two weeks (ie those in A switched to B and vice versa).

The women underwent a variety of tests at the beginning and end of each study period, including an overnight fast to determine resting metabolism and measurement (for three hours) of metabolic rate following consumption of a milkshake test meal, containing 50% of calories as carbohydrate, 15% as protein and 35% as fat.

The researchers found that while the average daily calorie intake remained the same, regardless of eating pattern, and resting metabolism after an overnight fast remained unchanged, the overall thermic effect of the milkshake meal was significantly higher following a regular meal pattern (A) than an irregular one (B).

And the researchers went on to conclude that the reduced thermic effect associated with irregular eating might be significant enough to lead to weight gain in the long-term!

These findings may help to explain what many bodybuilders striving for reduced body fat while maintaining sufficient calorie intake to train and recover have known intuitively all along: that several small meals consumed at evenly-spaced intervals throughout the day are preferable to irregular and variable consumption.

The same research group went on to analyse the health implications of irregular v regular eating patterns by measuring circulating glucose, lipids, insulin and uric acid in blood samples taken over a three-hour period following the consumption of a high-carbohydrate test meal⁽²⁾. They found that peak insulin levels were significantly higher after irregular eating, as were markers of total insulin secreted, indicating a degree of insulin resistance. Moreover, levels of LDL cholesterol (the ‘bad’ sort, associated with heart disease) were also raised by irregular eating patterns.

The researchers concluded: ‘An irregular meal frequency appears to produce a degree of insulin resistance and higher fasting lipid profiles, which may indicate a deleterious effect for cardiovascular risk factors. Quite apart from the health implications, optimum insulin function is vital for recovery, growth and regulation of energy in hard-working bodies.

The message for athletes seems to be that careful forward planning of meals and snacks is more important than we had previously realised; the evidence suggests that it’s not just what and how much we eat that matters, but also when and how we eat it!

Andrew Hamilton

References

1. International Journal of Obesity, vol 28, no, 653-660
2. International Journal of Obesity, vol 58, no 7, 1071-1077

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