Exercise Blunts Insulin Resistance & Hyperlipidaemia Due to 7-Day +50% / +75% Overfeeding in Athletic Young Men

Gluttony is one of the 7 sins - no wonder that eating more than you "deserve" makes you ugly and sick.

Everybody knows that "physical activity is good for you". Some, like me, even go so far to say that it's necessary - at least for those of us who plan to lead a healthy life into their old age. The classic idea that many of its beneficial effects are related to the ability of physical exercise to fix your dietary lapses on the other hand, has turned out to be - at best - part of of the 'health equation' (see "The Fallacy of Working Out to Burn Energy" | read more).

Nevertheless, Jean-Phillipe Walhin and his colleagues from the University of Bath demonstrate in their most recent paper that the ability of exercise to blunt the ill health effects of short-term overfeeding is a non-negligible part of the 'health equation'.

Don't worry this is a human trial!

For their experiment Jean-Philippe Walhin, Judith D. Richardson, James A. Betts, and Dylan Thompson recruited healthy, "habitually active" male volunteers aged 25 ± 7 years. Eligible were only men who participating in structured vigorous-intensity exercise for thirty minutes or more, at least three times per week. After 26 athletic young men who met these criteria were found, they were randomized to one out of two groups by a third party and put on ...

• a fixed energy surplus for 7 days on which their physical activity was restricted (SUR), or
• the same energy surplus and general activity limit, but w/ daily cardio training (SUR+EX). 

The target increase in energy intake for both groups was 50%. Both groups also reduced their general daily activity to ≤4000 steps. Contrary to the SUR group, for which the 4,000 steps / day was all they got in terms of 'exercise', the SUR+EX group had to perform a daily bout of 'vigorous-intensity' treadmill running (5 min warm-up at 60 % V O2maxthen 45 min at 70 % V O2max). To ensure compliance, all subjects had to wear a pedometer (Yamax, Japan).

The energy expenditure was compensated!

As a regular here at the SuppVersity you will be aware that this study would hardly have made it into the SuppVersity articles, if that, i.e. one group eats + 50% and sits around all day, while the other consumes the same amount of energy and works out, would be all the experiment had to offer. What makes the paper actually interesting is something the scientists marked as "critically" in the abstract to their paper:

"[T]he SUR+EX group received additional dietary energy intake to account for the energy expended during exercise; thus maintaining a matched energy surplus." (my emphasis in Walhin. 2013)

Practically speaking this meant that the subjects in the SUR + EX group had to eat even more food to achieve an additional +25% increase in energy intake that was meant to compensate for the extra energy the subjects in this group would be burning during their daily exercise sessions.
If we take the 'energy bonus' of +25% into account, we are thus dealing with a comparison of a +50% energy intake diet without exercise and a +75% energy intake diet with exercise. Whether or not this would yield a "matched energy surplus" is something I personally don't care about.

Why? Well, outside of a metabolic ward you got to rely on a bunch of funky equations and the hilariously stupid assumption that energy intake and energy expenditure would not depend on each other. Against that background, it does not really matter that the data in Figure 1 indicates that the energy surpluses ended up being ca. 18% apart. In view of the unreliability of these kinds of  'energy in vs. energy out' calculations, this is still close enough to qualify the energy surplus as being roughly identical.

Figure 1: Total energy intake and calculated energy surplus (in kcal/day) in the SAR vs. SAR+EX groups (Walhin. 2013)

To assess the effects of this protocol, fasted blood samples and abdominal subcutaneous adipose tissue biopsies were obtained and oral glucose tolerance tests conducted at baseline and during a follow up visit to the laboratory one week later. Instead of reiterating the verbose summary of the corresponding findings, I have compiled a comprehensive overview of the most significant (not necessarily statistically, by the way) study outcomes in Figure 2:

Figure 2: Relative changes (% of baseline) in glucose + fat metabolism, adiponectin, leptin and alanine transaminase levels (the latter a considered a measure of liver strain) during one week of overfeeding (Walhin. 2013)

As you may guess based on the relative changes to the parameters of glucose management (see Figure 2, left), the insulinaemic responses to a standardized glucose load increased 2-fold from baseline to follow-up in the SUR group (Δ17 ± 16 nmol/120min; P=0.002). In the SUR+EX group, on the other hand, the single week of (even more pronounced) gluttony did not lead to comparable increases in insulin resistance or glucose intolerance (SUR+EX group → Δ1 ±6 nmol/120min).

Not shown in Figure 2 are the results of the gene essays the scientists conducted. Unsurprisingly, the results are not significantly different. It's once more the "lazy" SUR group, in whom the gene expression in the fat (=adipose) tissue turned from 'neutral' to 'pro-diabetic and -dyslipidaemic:

"Seven of 17 genes within adipose tissue were differentially-expressed in the SUR group; expression of SREBP1c, FAS and GLUT4 was significantly up-regulated and expression of PDK4, IRS2, HSL and VISFATIN was significantly down-regulated (P≤0.05)." (Walhin. 2013)

It is thus no wonder that AMPK, one of the most important markers we have, when we are talking about issues with blood glucose management (learn more), or, even more specifically, the ratio of phosphorylated to unphosphorylated protein was also significantly down-regulated elusively in the SUR group (P=0.005).
References:

• Walhin JP, Richardson JD, Betts JA, Thompson D. Exercise counteracts the effects of short-term overfeeding and reduced physical activity independent of energy imbalance in healthy young men. J Physiol. 2013 Oct 28.