Study under review: Skipping Breakfast Before Exercise Creates a More Negative 24-hour Energy Balance: A Randomized Controlled Trial in Healthy Physically Active Young Men.
Despite exercise increasing daily energy expenditure, and thus, in theory, creating negative energy balance, interventions that have focused on using exercise as a tool for weight loss have revealed lower weight loss than predicted based on the amount of extra energy expended. This is mostly due to the fact that some people compensate for the energy expended during exercise by consuming more calories, thus negating any effect of exercise on energy balance. Another compensatory behaviour that can occur in response to exercise is a reduction in non-exercise physical activity, meaning that people move less in their daily lives. These responses limit the ability of exercise to cause negative energy balance and weight loss. On the other side of the equation, skipping breakfast has been shown to promote a lower energy intake compared to eating breakfast (see Study Deep Dives #53, Volume 1, “Will eating breakfast keep you lean?”), but it appears to reduce morning physical activity compared to eating breakfast in lean and obese participants.
It has been proposed that the body’s glucose stores, in particular hepatic glycogen (the primary source of blood glucose between meals), plays an important role in regulating energy intake (serving as a kind of “sensor” of energy availability). As depicted in Figure 1, if glucose oxidation is too high, and hepatic glycogen levels are reduced, this could trigger a compensatory increase in energy intake to maintain levels of glycogen above certain levels. Accordingly, there is some evidence in humans showing that higher levels of glucose oxidation during exercise are associated with higher energy intake after exercise. Therefore, increasing the proportion of energy derived from fat oxidation during exercise (and reducing glucose oxidation), like what happens during fasted exercise, might prevent the compensatory increase in energy intake.
The main goal of the study under review was to assess the role of carbohydrate availability during morning exercise sessions on 24-hour energy balance, in normal weight men.
Weight loss interventions that have used exercise as a weight loss tool have shown mixed results as a consequence of either energy intake compensation or a subsequent reduction in non-exercise physical activity. There is some evidence that suggests how much glucose one uses during exercise is associated with how many calories one consumes after exercise. As performing exercise in the fasted state reduces the relative contribution of glucose to the overall energy demands of exercise, exercising before breakfast, or “fasted cardio,” might prevent or at least ameliorate compensatory increases in energy intake.
Other Articles in Issue #60 (October 2019)
Vitamin D on the mind: can vitamin D help with Alzheimer's?
This randomized controlled trial suggests that supplementation has a surprisingly strong effect on aspects of cognition in people with mild Alzheimer's disease. But are the results a little too surprising?
Mini: Is vitamin D supplementation useful for pregnant women?
We've previously covered evidence suggesting that pregnant women supplementing with vitamin D have a lower risk of giving birth to babies with low birthweight. This Cochrane review suggests vitamin D may have other benefits as well.
Can vitamin D impact mortality?
This meta-analysis suggests that if it does, the effect size on all-cause mortality is pretty darn small. However, supplementation may reduce the risk of dying from cancer.
Does plate size matter?
Previous research looking at whether shrinking one's plate actually shrinks one's food intake has been equivocal. This well-designed study sheds some stronger light on the issue.
Supplementing spirulina for metabolic maladies
This meta-analysis synthesizes the latest evidence concerning spirulina's ability to make a dent in the metabolic syndrome.
Red flags in study design cast doubt on soy supplementation study results
Want to know some reasons why we don't usually cover studies looking at proprietary supplement blends? Then read on.
Interview: Suzanne Robotti, Founder of MedShadow
In this interview we chat with the founder of MedShadow, a nonprofit whose mission is to provide the information needed to weigh the risks and benefits of healthcare treatments.