The blog post from New York Times talks about the effect of high intensity interval exercise on appetite control and food intake. The author cites findings from two published studies to demonstrate that young men ate less when they performed high intensity workout compared to when they did no or moderate level exercise. The effect on appetite was evaluated by looking at biomarkers of hunger and fullness. The effect on appetite reduction lasted for a day following rigorous workout. This finding is encouraging for people who want to lose weight.
Keywords: intensity, interval, appetite, aerobic capacity
The phenomenon of alternating between highly strenuous and challenging exercise and rest or relaxation is called interval training. Interval training has become one of the most popular methods of doing exercise among athletes, runners and rest of the population. A high intensity workout is “short, intense workouts, usually in the form of intervals that intersperse bursts of hard effort with a short recovery time” (Reynolds, 2013). In other words interval training is a workout that requires the participant to do exercise at a fast or intense pace. This fast paced activity is followed a short period of rest or activity performed at a slow or moderate speed. The overall aim of this kind of workout is to increase the cardiovascular strength and fitness. A number of studies have demonstrated that this kind of rigorous exercise has a number of health benefits, including an increase in the overall aerobic health. Interval training also shows improvement in blood pressure level and reduction in insulin resistance. The benefits of high interval exercise done for small duration are similar to those observed with moderate exercise done for longer duration of time. It is believed that doing moderate exercise over a prolonged period of time allows the cells to get attuned. On the other hand, a workout consisting of interval training gives the cells a shock or jolts that result in improvement in aerobic activity. However, “the effect of high interval training on food intake and weight loss was not clearly understood until now” (Reynolds, 2013).
Researchers from the University of Western Perth in Australia published a study in the International Journal of Obesity, in which they evaluated the difference in appetite or desire to eat following either strenuous or low intensity exercise. They enlisted 17 men in their 20s and 30s who were overweight. The men were supposed to visit to the laboratory at the University of Western Perth on four separate days. They were made to take part in a physical activity sessions that ranged from light to intense on different days. In the first session the men read books or rested leisurely for 30 minutes. The next session involved the men riding exercise bikes at a pace that resulted in achieving “65% of maximum aerobic capacity” (VO2max orVO2peak) (Reynolds, 2013). The third session was more challenging for the participants. They rode the bike for a minute at 100% of their aerobic capacity (VO2peak), followed by spinning at moderate speed for the next four minutes. They were supposed to follow this routine for 30 minutes. The last of the exercise session was the most physically demanding. The participants were made to ride the bikes at a speed that allowed them to attain 170 % of their (VO2peak) for 15 seconds followed by cruising on the bike for a minute at barely 30% of their maximum aerobic capacity. Following completion of each of the four sessions, blood was drawn from the volunteers to measure the level of chemicals known to affect hunger and appetite. Following the completion of each session that lasted 30 minutes, the participants were given liquid breakfast to eat. Another hour and ten minutes later, the participants were allowed to eat plain sweetened porridge to their heart’s desire. The porridge was made without any strong aroma or smell to prevent the effect of factors other than their own appetite for the served food. In order for only their appetite, to control the amount of food they ate, the porridge was devoid of any pleasant smell. The researchers made some very interesting observations after the completion of the four workout sessions. Men who had rested for 30 minutes or pedaled at a modest speed ate sumptuous amount of the porridge. However, men who had participated in the interval exercise sessions demonstrated significantly lower appetites as compared to the first two sessions. The workout session that required the participants to ride the bikes in the most demanding capacity resulted in the participants consuming the least amount of porridge. It seemed that were merely picking at their food. The most challenging biking session also resulted in the lowest level of the hormone ghrelin in the participants. Ghrelin is a hormone associated with stimulation of a person’s appetite. The levels of ghrelin are usually elevated prior to a meal and go down after a person has eaten. These most challenging, interval workout sessions also resulted in “higher blood sugar and lactate levels” in the participants (Reynolds, 2013). Both the blood sugar and lactate levels are known to lessen the desire to eat. The fact that lower levels of blood glucose and lactate levels were observed indicated a reduction in the study subjects’ appetite. The lowered appetite following the high interval workout continued the next day. This was observed from the food diaries the study subjects maintained. Men from the most grueling session (15 seconds high intensity session-followed by a minute rest) ate the least number of calories as opposed to days following the other three sessions that required them to work at more relaxed capacity.
Another study published in the journal PLoS One which looked at the relation between appetite and exercise intensity, mirrored the findings from the first study. This study was done by recruiting obese teenage boys. The boys were required to make three visits to the study site. In each visit they spent 24 hours in an enclosed metabolic chamber which was capable of constantly measuring their energy input and output. According to the authors of the study the obese boys made three visits for the study. In the first visit they rested throughout their stay, on their second visit to the study center they exercised on a spinning bicycle at a fairly relaxed or moderate pace. The third visit required the subjects to spin on the stationary bikes at a very fast pace. The subjects in the second and third visit were required to spin until they had burnt about 330 calories. The time required to burn 330 calories would vary between subjects pacing at slow or fast rate. At the end of the session the boys were offered a buffet rich in various food choices. The teenage boys consumed large portions of meals. They more than replenished the calories they had consumed while exercising on the bikes. However, in this study, as was observed in the previous one, after the intense session, “they ate smaller amount of food compared to when they did not work out or worked out at moderate pace” (Reynolds, 2013). They consumed almost 10 percent calories fewer than after resting or pedaling at moderate speed.
According to the results obtained from the two studies, high intensity workout curbs the appetite of the subject. The blog article cites the author of first study, Aaron Sim from the University of Western Australia, who directed the study looking at effect of interval exercise on overweight men. “Intense exercise leads to a short-term suppression of food intake” (Reynolds, 2013). The finding that exercise can lower a person’s appetite would be welcomed by people who are trying to lose weight and achieve a healthy weight.
It is important to remember that these studies were performed on a very small group of participants and involved only one intensity exercise per session. The long term effects of “high intensity exercise on a large population of participants are unknown” (Reynolds, 2013). In order to provide robust results the studies need to be repeated on a large number of participants. According to Mr. Sim, the author of first study the long term effect of intense training on overall weight-management is not clear. It is possible that weeks and months of high intense exercise may not result in sustained weight loss. The two studies “recruited young overweight male participants who did not seem to mind the highly challenging and physically demanding interval training biking session” (Reynolds, 2013). They seemed to enjoy the strenuous exercise routine writes the author. It is also to be noted that to truly understand the effect of high intensity exercise on appetite reduction on women, older men or people of either gender who are normal weight, the studies need to be repeated for an extended period of time on a diverse group of participants.
Reynolds, G. (2013, Sep 13). How exercise can help us eat less. The New York Times.com. Retrieved October 1, 2013 from, http://well.blogs.nytimes.com/2013/09/11/how-exercise-can-help-us-eat-less/?_r=0