Working out on an empty stomach could amplify the health benefits of the activity, according to a well-timed new study of the interplay of meal timing, metabolic health and moving. The study, which involved sedentary men and moderate cycling, suggests that whether and when we eat may affect how exercise affects us.
In general, any exercise improves our health. But a wealth of recent science and personal experience indicate that different people can respond to similar exercise routines in different ways. Even if everyone completes the same amount of exercise, some people become more fit than others, or lose more weight, or gain greater control of their blood sugar.
Most exercise scientists believe that our genetics, diets, physiques, temperaments and other subtle aspects of our lives act in concert to shape how our bodies react to exercise.
But some researchers suspect meal timing matters as well. Working muscles need fuel during exercise, mostly in the form of sugar (glucose) or fat. That fuel can come from our most recent meal, once its component sugars and fats reach our bloodstreams, or from our bodies’ stores of fats and sugars. We all have such stores, especially of fat, some of it residing in our muscles and marbling them like pricey sirloin.
This muscle fat becomes problematic if we accumulate too much of it. Fatty muscles do not respond well to the hormone insulin, which directs sugar from the blood into the muscles. As a result, excess fat can contribute to insulin resistance, high blood sugar levels and increased risks for Type 2 diabetes and other metabolic conditions.
So, researchers at the University of Bath in England and other institutions began to wonder whether meal timing might influence how much muscle fat we burn during exercise, which would then affect the long-term metabolic consequences of exercise and help to explain, in part, why some people get more out of exercise than others.
To look into those issues, they recruited 30 overweight, sedentary men. (They plan to do a follow-up study with women.) The researchers tested the men’s fitness and insulin sensitivity and then divided them into three groups.
One, as a control, continued their usual lives. The other two groups started supervised exercise in the morning three times a week, riding stationary bicycles at a moderate pace while wearing monitors and masks that tracked their heart rates and the amount of fat and sugar they burned. The researchers also asked them periodically how they felt while riding.
One exercise group also downed a vanilla-flavored shake two hours before their ride (with no other breakfast) while the other group swallowed a similar-tasting placebo drink, containing water, flavoring and no calories. In other words, the placebo group rode on an empty stomach, but did not know it.
After exercise, each rider received the drink he had not previously swallowed. The riders who had fasted got the shake and the other group the placebo.