Who doesn’t want to get the biggest possible weight-control and metabolic benefits from diet and exercise?
There’s good evidence that two factors can significantly affect weight control and metabolism: the timing of exercise in relationship to meals — especially breakfast — and the proportions of fat, carbs, protein in a breakfast.
Back in 2014, scientists from the University of Missouri reported the results of two clinical trials that probed the effects of a breakfast's nutritional makeup on weight control and metabolic health.
And the results of those trials suggest that high-protein breakfasts can aid weight control and enhance metabolic health: see Can Paleo-Style Breakfasts Curb Food Cravings? and High-Protein Breakfasts Help Blood Sugar Control.
Let’s turn to another key influence on weight control and metabolic health: the timing of exercise in relation to breakfast.
As we’ll see, the new findings support prior evidence suggesting that — rather than waiting to eat breakfast — it’s wise to work out first.
Prior, positive findings prompted the new trial
Scientists from Britain’s universities of Bath and Birmingham have been researching how the body responds to exercise undertaken either before or after eating breakfast.
We covered a clinical study they published in 2017, which found that eating before exercise caused men’s bodies to rely on recently consumed calories rather than stored fat to fuel their workouts: see Feast or Fast Before Exercise to Boost Fat-Burning?.
That finding fits with those of a 2012 evidence review, whose French and British authors concluded that exercising before eating raises your resting metabolic (calorie-burning) rate and directs your muscles to favor fat over carbohydrates as fuel (Thompson D et al. 2012).
Professor Dylan Thompson of Bath University — who co-authored the 2012 evidence review and the clinical trial we’re reporting on today — expressed the meaning of the review’s findings: “Just looking at the weighing scales when you increase your physical activity will only tell you part of the story — your adipose tissue may be doing some quite amazing things underneath, even without getting any smaller.”
Last year, the Bath-Birmingham team reported the results of a clinical study involving 12 healthy male volunteers, which showed that eating a high-carb breakfast (porridge with milk) before exercise appeared to “prime” the men’s bodies to burn carbohydrates during exercise and more rapidly digest food after working out (Edinburgh RM et al. 2018).
In addition to the carbs in their breakfast, some of the carbs the participating men burned were carbohydrates stored in their muscles, called glycogen. The British researchers speculated that the body’s effort to rebuild its muscle glycogen stores might explain why the participants cleared sugar (glucose) from their blood more rapidly after lunch.
New British trial sees benefits to exercising before breakfast
The joint Bath-Birmingham research team recently reported the results of a clinical trial designed to detect the metabolic effects of exercising before breakfast versus exercising after breakfast (Edinburgh RM et al. 2019).
They recruited 30 men who were either obese or overweight to participate in two different studies:
The British team also compared the metabolic effects seen in the two test groups to those measured in members of a control group who made no lifestyle changes.
And the results showed that — compared with the men who exercised after breakfast — the men who exercised before breakfast burned twice as much body fat.
The researchers attributed the increased fat-burning seen in the pre-breakfast exercise group to lower insulin levels during exercise, which prompted their bodies to burn more of the fat stored in their fat tissue and muscles.
While the men assigned to the pre-breakfast exercise group for six weeks did not shed more pounds than the men in the post-breakfast exercise group, the results showed that pre-breakfast exercise exerted “profound and positive” effects on men’s metabolic health.
Specifically, the bodies of the men in the pre-breakfast exercise group responded to the insulin released in response to breakfast more healthily, thereby keeping blood sugar levels under control and potentially lowering the risk of diabetes and heart disease.
The muscles of the pre-breakfast exercise group also showed greater increases in proteins that help transport sugar (glucose) from blood to the muscles.
Somewhat surprisingly, the insulin responses to meals seen in the post-breakfast exercise group were no healthier than the insulin responses seen in the control group.
As study co-author Dr Javier Gonzalez of the University of Bath explained, “Our results suggest that changing the timing of when you eat in relation to when you exercise can bring about profound and positive changes to your overall health.”
And Dr. Gonzalez stressed an important finding: “The group who exercised before breakfast increased their ability to respond to insulin, which is all the more remarkable given that both exercise groups lost a similar amount of weight and both gained a similar amount of fitness.”
This study involved only men, but the British researchers say that future studies will include women, to see whether their bodies respond differently to pre-breakfast and post-breakfast exercise.