A 90-minute walk lowered triglycerides and improved blood vessel function in a small group of lean and obese men, and the benefits persisted into the following day, even after participants ate a fatty meal, according to a new study in the Dec. 21, 2004 issue of the Journal of the American College of Cardiology.
“Just one brisk walk substantially improved blood vessel function both before and during the hours after eating a fatty meal, and the exercise improved the body’s handling of dietary fat to the same extent irrespective of whether someone was lean or obese,” said Jason M. R. Gill, Ph.D., at the University of Glasgow, Scotland.
“The differences observed in blood fat levels and in blood vessel function following just one workout are remarkable, particularly as these were evident for at least 24 hours after completion of exercise,” he said. “Recent research has shown that blood vessel function is impaired for a few hours after eating fatty food, and this may be one reason why the rise in blood fats seen after eating seems to contribute to the development of heart disease. As we have known for some time that exercising before eating fatty food reduces this rise in blood fat levels, we thought that a workout before eating a fatty meal could help to prevent the post-meal decline in blood vessel function.”
The researchers studied 10 lean and 10 obese middle-aged men. Each man was tested twice for his response to a fatty meal, with the tests performed a week or two apart. On the afternoon before one of the tests, each man walked on a treadmill for 90 minutes. No exercise was done the day before the other test.
Exercise reduced triglyceride concentrations by 25 percent both before and after the fatty meal. Similar responses were seen in both the lean and the obese men.
Particularly striking, according to Dr. Gill, was the effect of the long walk on the functioning of tiny blood vessels in the forearms of subjects as measured by laser Doppler imaging. Overall, the responsiveness of the endothelium, measured before the fatty meal, was 25 percent better following the treadmill walk. The endothelium is a single layer of cells that lines the inner wall of blood vessel. It provides an important defense against the build-up of fatty deposits inside blood vessels.
Although the fatty meal reduced blood vessel function whether or not the men had exercised the previous afternoon, the decline was not as great after exercise. Endothelium-dependent function was 15 percent higher and endothelium-independent function was 20 percent higher in the exercise trial than in the control trial, and again the benefits were seen in both the lean and obese men.
While the benefits of regular physical activity are well-established, the researchers say this study suggests some possible explanations for the protective effects: that exercise can both improve the way the body metabolizes food and help blood vessels resist the harmful effects of fatty foods. This trial also demonstrated that a single exercise session can provide immediate benefits that last at least a day.
“Ninety minutes of exercise is a long time, but it is important to note that the exercise was not strenuous and even obese men who were unused to exercise completed the walk without difficulty. Having said that, we appreciate that many people will struggle to fit this amount of exercise into their busy schedules. The good news is that we have previously shown that as little as 30 minutes of exercise has a beneficial effect on the blood fat responses following a fatty meal and that accumulating exercise in two or three short sessions throughout the day has the same beneficial effect in this respect as one longer session. The size of the benefit is related to the number of calories burned during exercise, so any exercise you do will be beneficial, it’s just that if you do twice as much, you get twice the benefit,” Dr. Gill said.
Dr. Gill noted that this study, which was funded by the British Heart Foundation, involved only 20 men, so he would like to see the findings confirmed by larger studies.
David S. Celermajer, M.D., Ph.D., at the University of Sydney, Australia, who was not connected to this study, called it an excellent and interesting article. He noted that while most such studies test people after they have been fasting for many hours, this study looked at what happened in people under more typical conditions, when they have recently eaten a meal.
“Therefore the current study addresses a real ’area of need’ in research, as it studies changes in vessel function after a meal and investigates the effect of a simple intervention, a long period of low-grade exercise before the meal,” Dr. Celermajer said. “As the authors write, the major novel finding of this study is therefore that a single session of moderate exercise, rather than most previous studies, which have examined the effects of chronic exercise, can significantly improve small vessel vasodilator function. This suggests that exercise can have acute as well as chronic benefits on the vasculature.”
Dr. Celermajer said that although this study probably won’t prompt any changes in exercise recommendations, it does put a spotlight on research into the effects of exercise on blood vessel function and how the body processes food.
“It would be clearly of interest to examine whether shorter bursts of exercise such as 10 to 15 minutes, which might be clinically applicable, have similar benefits on post-meal vascular and metabolic factors, compared with the 90-minute sessions studied in this paper.”