Burning a couple of hundred kcal extra a day by exercising more is a great way to lose weight. Reducing the amount of carbohydrates in your food is another good way to lose weight. It’s a shame you can’t combine the two – because if you’ve got a low blood sugar level your muscles can’t perform well and you can forget doing exercise. Or not? Nutritionists at the University of South Australia have a different view of the matter.
No, a low-carbohydrate diet isn’t necessarily the only way to lose weight, and yes, low-carb weight loss is fine. For an overview of all the articles on low-carb diets on this weblog, click here.
Many trainers are not at all in favour of low-carbohydrate eating patterns. Athletes need carbs, they say. Without glucose athletes don’t have the energy to train. And trainers say this not because they are stupid, but because they listened carefully when they did their training course. It’s still in textbooks and course material – and all the information is based on good scientific research.
The researchers at the University of New South Wales took another good look at the effect of aerobic training on pain tolerance. They got a dozen students to cycle at One disadvantage to these studies is that they are all of short duration. In practice, a body that’s used to a high-carb diet needs a few days – and sometimes even a few weeks – to get used to a diet in which the energy is derived mostly from fats and proteins.
The Australians wanted to describe the long-term effects of a low-carb diet on performance capacity, so they put a group of about twenty overweight adults on a low-carb diet for a year [LC]. An equal-sized control group got a high-carb diet [HC]. Both low-carb and high-carb diet provided the subjects with a couple of hundred calories less than they burned.
After a year both groups had lost about the same amount of fat. The differences between the two groups were not significant.
During the year that the study lasted the subjects did not do any extra sport. Before they started the diet and at the end the researchers tested their physical condition on a treadmill and measured their muscle strength. The weight loss made the subjects in both groups a little fitter; both groups performed equally well.
The people on the low-carb diet burned more fat during moderately intensive exercise on the treadmill. The high-carb diet had the opposite effect. The difference between the effect of the low-carb and the high-carb diet was statistically different.
The subjects in both groups burned the same number of kcals on the treadmill.
“Compared to a high carb diet, long-term consumption of a low carb diet did not impair exercise tolerance or exercise capacity in overweight and obese individuals”, the researchers conclude. “A low carb diet shifted fuel utilization during submaximal exercise to favor fat oxidation with no effect on rating of perceived exertion.”
“Overall, these data suggest that compared to a high carb diet, prolonged consumption of an low carb weight loss diet should not impact adversely on physical function or the ability to perform exercise.”
Long-term effects of a very low-carbohydrate weight loss diet on exercise capacity and tolerance in overweight and obese adults.
Compare the long-term effects of an energy-restricted very low-carbohydrate, high-fat (LC) diet with an isocaloric high-carbohydrate, low-fat (HC) diet on exercise tolerance and capacity in overweight and obese adults.
Seventy-six adults (25 males; age 49.2 ± 1.1 years; BMI 33.6 ± 0.5 kg/m(2)) were randomized to either a hypocaloric (6-7 MJ/day) LC diet (35% protein, 4% carbohydrate, 61% fat) or isocaloric HC diet (24% protein, 46% carbohydrate, 30% fat) for 52 weeks. Pre- and postintervention, participants’ body weight and composition, handgrip, and isometric knee extensor strength were assessed and participants performed an incremental exercise test to exhaustion.
Forty-three participants completed the study (LC = 23; HC = 20). Overall, peak relative oxygen uptake increased (+11.3%) and reductions occurred in body weight (-14.6%), body fat percentage (-6.9% [absolute]), isometric knee extensor strength (-12.4%), handgrip strength (-4.5%), and absolute peak oxygen uptake (-5.2%; p ? 0.02 time for all) with no diet effect (p ? 0.18). During submaximal exercise, rating of perceived exertion did not change in either group (p = 0.16 time, p = 0.59 Time × Group). Compared to the HC diet, the LC diet had greater reductions in respiratory exchange ratio (LC -0.04 ± 0.01, HC -0.00 ± 0.01; p = 0.03), and increased fat oxidation (LC 15.0 ± 5.3% [of energy expenditure], HC 0.5 ± 3.9%; p = 0.04).
In overweight and obese patients, an LC diet promoted greater fat utilization during submaximal exercise. Both an LC diet and an HC diet had similar effects on aerobic capacity and muscle strength, suggesting that long-term consumption of an LC weight loss diet does not adversely affect physical function or the ability to perform exercise.
PMID: 24988413 DOI: 10.1080/07315724.2014.911668 [PubMed – indexed for MEDLINE]