Many studies have demonstrated that the timing of meals and exercise is important for glycogen loading, muscle building and improved nutrient uptake and utilization by the body. These studies have shown that even a single bout of exercise can change the body’s hormonal response that in turn positively affects nutrient metabolism in skeletal muscle, liver and even adipose (fat) tissue. Some studies have looked at these same factors in relation to triglyceride (TG) levels in the blood and now, importantly so, because recent evidence suggests that elevated TG levels several hours after a meal may be an independent risk factor for cardiovascular disease (CVD). However, most studies to date have looked at the effects of moderate to vigorous running, cycling, brisk walking and resistance exercise, singularly and timed far prior (sometimes 12-16 hours) to ingestion of a meal. In a recent study, researchers decided to look at exercise on the day of a high-fat meal. Additionally, because recent recommendations for better health and disease prevention include both aerobic and resistance exercise, they wanted to look at the effects a combined program might have.
Subjects and Timing of Meals: Ten healthy young subjects (4 men and 6 women) between 21-15 years of age, who were not regular exercisers, and of normal weight and body fat were recruited. Three trials were completed: rest, exercise before meals, and exercise after meals. Breakfast was controlled for and pre-meal exercise was at 11:00 a.m. and meal intake at 12:00 p.m. For post meal exercise the meal was eaten at noon and exercise was done one hour after eating. Subjects were asked not to eat or drink anything except water after 10 p.m. at night. The meals had very slight differences in ratios for men and women but were each about 38% fat (high fat), 10 % protein, and 51% carbohydrates.
Exercise Design: Of interest in this study were the exercise intensity (low) and the results of combining a cardiovascular and resistance training bout. Subjects walked 1.2 miles (2 km) in 31 to 32 minutes with a rating of perceived exertion (RPE) of 9.6 (low intensity). After a 2 minute interval, participants performed light resistance exercise of 15 repetitions with 5 to 6 pound dumbbells except for the push-up and leg raise for the following exercises: squats, shoulder press, shoulder lateral side raise, bent over rowing (upper back), biceps curls, triceps extensions, side bends, trunk twisting (spine rotations), push-ups and leg raises.
Results: TG concentrations were reduced by 25% with pre-meal exercise and dramatically reduced by 72% with post-meal exercise. These results were for low intensity and short duration exercise bouts. In previous studies a single bout of exercise before meal ingestion was found to reduce TG by 16% to 51% 6 to 8 hours after a high fat meal. However the exercise was relatively high intensity (> 60%) of maximum oxygen uptake for 30 to 90 minutes or low intensity exercise for 180 minutes. So the intensity and duration were much longer and prior to meals. This current study shows that good results are available for pre-meal exercise and extremely impressive for post meal exercise after a high fat diet.
Discussion: With the recent evidence that triglycerides may play an even greater role in CVD, reducing TG levels especially the elevation that takes place after a high fat meal may have a significant impact on preventing CVD. What is promising about this study is that not only did exercise have such a significant effect but that it was a short bout of exercise of low intensity. Most people of any age could participate in this combined walking and light resistance training (5 to 6 pound dumbbells). It is “doable” physical activity that could bring significant benefits to those with metabolic syndrome and higher levels of fasting TG, and those at higher risk for CVD. What is also interesting and of significance is that the timing of exercise may strength the potential impact that it has.
Aoi, W. (2013). Combined light exercise after meal intake suppresses postprandial serum triglyceride. Medicine & Science In Sports & Exercise, 45(2), 245 - 252.