A new study published in the American Journal of Physiology has found that 30 minutes of daily aerobic exercise training are as good as, and even slightly more effective than, 60 minutes to achieve the same loss of weight and body fat.
In fact, the researchers found that “On average, the men [in the study] who exercised 30 minutes a day lost 3.6 kg [about 8 pounds] in three months, while those who exercised for a whole hour only lost 2.7 kg [about 6 pounds]. The reduction in body mass [fat] was about 4 kg [a little over 8.5 pounds] for both groups,” according to study author Mads Rosenkilde, a PhD student in the Department of Biomedical Sciences at the University of Copenhagen, Denmark.
The new study has been published in the American Journal of Physiology.
“The amount of weight loss induced by exercise is often disappointing,” the study authors noted in an introduction. “A diet-induced negative energy balance triggers compensatory mechanisms, e.g. lower metabolic rate and increased appetite. However, knowledge about potential compensatory mechanisms triggered by increased aerobic exercise is limited,” they noted.
The objective of the new study was “to examine the effects of increasing doses of aerobic exercise on body composition, accumulated energy balance, and the degree of compensation,” the researchers wrote.
The Study; Methodology
For thirteen weeks, a research team at the University of Copenhagen, Denmark, followed 60 healthy sedentary moderately overweight young men in their efforts to lose weight through exercise.
For a period of three months and one week, 21 of the men were assigned to a group that engaged in 30 minutes of aerobic exercise each day (burning 300 kcal/day of energy), while 22 of the men were assigned to a group that engaged in 60 minutes of aerobic exercise daily (burning 600 kcal/day of energy). Eighteen of the participants were assigned to a sedentary control group. All assignments were made randomly. All of the participants wore a heart-rate monitor and calorie counter during all exercise.
“All training sessions were planned to produce a light sweat, but participants were expected to increase the intensity and give it gas three times a week,” Mads Rosenkilde, the author, explained in a News Release issued by the University of Copenhagen.
The “research results show that 30 minutes of exercise hard enough to produce a sweat is enough to turn the tide on an unhealthy body mass index,” the University of Copenhagen’s news release said.
The researchers found that “body weight … and fat mass … decreased similarly in both exercise groups.” In fact, the group that exercised 30 minutes per day did slightly better in weight loss and reduction in body fat mass than the group that exercised for 60 minutes a day.
Those who exercised 30 minutes per day lost an average of 3.6 kg (approximately 8 pounds) of weight and reduced their body fat by 4.0 kg (8 pounds, 13 oz.), while those who exercised 60 minutes per day lost an average of 2.7 kg (approximately 6 pounds) of weight and reduced their body fat by 3.8 kg (8 pounds, 6 oz.) over the same thirteen week period.
“Although the exercise-induced energy expenditure in HIGH [the group exercising 60 minutes a day] was twice that of MOD [the group exercising 30 minutes a day] the resulting accumulated energy balance, calculated from changes in body composition, was not different (MOD: -39.6Mcal, HIGH: -34.3Mcal, NS),” the researchers found.
“Energy balance was 83% more negative than expected in [the group exercising only 30 minutes a day], while it was 20% less negative than expected in [the group exercising 60 minutes a day],” the authors wrote.
“No statistically significant changes were found in energy intake or non-exercise physical activity that could explain the different compensatory responses associated with 30 vs. 60 min of daily aerobic exercise,” the researchers noted.
“Participants exercising 30 minutes per day burned more calories than they should relative to the training program we set for them. In fact we can see that exercising for a whole hour instead of a half does not provide any additional loss in either body weight or fat,” the principal author, Mads Rosenkilde, noted.
“The men who exercised the most lost too little relative to the energy they burned by running, biking or rowing. 30 minutes of concentrated exercise [gave] equally good results on the scale,” Mr. Rosenkilde explained.
“In conclusion, a similar body fat loss was obtained regardless of exercise dose [whether 30 minutes a day or 60 minutes a day of aerobic exercise]. A moderate dose of exercise [30 minutes a day] induced a markedly greater than expected negative energy balance, while a higher dose [60 minutes a day] induced a small but quantifiable degree of compensation,” the authors wrote.
The principal author, Mads Rosenkilde, postulated in the University’s news release that part of the explanation for the surprising results may be that “30 minutes of exercise is so doable that participants in the study had the desire and energy for even more physical activity after their daily exercise session.”
A further explanation — and the reason that increased exercise often produces a disappointing amount of weight loss relative to the increase in activity level — may be that a negative energy balance (where daily energy usage exceeds calories consumed) triggers “compensatory mechanisms,” such as lower metabolic rate and increased appetite. The higher dose of exercise [60 minutes a day] “induced a small but quantifiable degree of compensation,” the authors concluded.
In any event, Mr. Rosenkilde expressed surprise at the research results, and said that his goal now is to study the effects of other types of exercise.
“Another interesting scenario is to study exercise as a form of transport. Training is fantastic for your physical and mental health. The problem is that it takes time. If we can get people to exercise along the way – to work, for example – we will have won half the battle,” Mr. Rosenkilde said.
Meanwhile, perhaps knowing that you only need to exercise 30 minutes a day to make significant progress toward weight loss will help motivate more people to make the effort.
The entire research report of the new study is available in the American Journal of Physiology.
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