Low carbs not equal to low energy

Energy bars with low or moderate levels of carbohydrates may not actually help dieters lose weight as they promise, as overall energy contents are similar to that of higher carbohydrate bars, reports a US study.

Proponents of several diet plans - such as the Atkins and Zone diets - say low or moderate carbohydrate foods lead to less of an insulin spike in the blood after meals, which helps lead to people burning more fat and losing more weight. However, this new study, supported in part by Atkins Nutritionals, found that energy bars advertised as having low or moderate levels of carbohydrate do not actually reduce insulin levels in the blood as much as expected.

"The bottom line is that these energy bars may not contribute to weight loss, at least not in the way that manufacturers are advertising they do,"​ said Steven Hertzler, the study's lead author and an assistant professor of medical dietetics in the School of Allied Medical Professions at Ohio State University in the US. "The makers of these reduced carbohydrate bars add more protein and fat to the ingredients, but the overall energy content of such bars is similar to that of a higher carbohydrate energy bar.​

"None of the manufacturers of these low and moderate carbohydrate snack foods have the data to support the claim that their products do keep after-meal insulin levels low,"​ said Hertzler. "Our study shows these energy bars lead to an insulin response closer to what we see with high carbohydrate bars.​

"Eating carbohydrate and protein together causes an insulin response that favours the replacement of carbohydrate stores in muscles and in muscle protein repair immediately after exercise. However, high insulin levels also impair the ability to burn fat, an effect that dieters don't want,"​ continued Hertzler.

Hertzler and Yeonsoo Kim, a doctoral student in Ohio State's School of Allied Medical Professions, said they asked 20 adults to eat one of five test meals on five separate days: a low-carbohydrate energy bar (Atkins Advantage Bar); a moderate-carbohydrate energy bar (Balance Bar) which fits the nutritional philosophy of the Zone diet, which recommends a diet of 40 per cent carbohydrates, 30 per cent fat and 30 per cent protein; a high-carbohydrate energy bar (Power Bar); white bread, which is nearly all carbohydrate; and broiled, boneless chicken breast, which contains no carbohydrate.

The participants were instructed to fast for 12 hours prior to each meal. About 10 minutes before eating, blood samples were taken from each subject which gave the researchers baseline readings of blood glucose and insulin levels. Additional blood samples were taken periodically up to two hours after the subjects began eating their meals.

The researchers used white bread to compare the insulin responses caused by the other four meals as they said they knew what kind of insulin response to expect from it.

According to the researchers, compared to white bread, eating the low-carbohydrate bar lowered insulin by about a quarter. Insulin levels rose by more than a third after participants ate the moderate-carbohydrate energy bar, and increased nearly three-quarters after eating the high-carbohydrate energy bar. Eating chicken caused the lowest insulin response - resulting insulin levels were more than three-quarters lower than those caused by white bread.

The high-carbohydrate energy bar affected insulin levels just as expected. These kinds of snack foods cater to people who want a sharp increase in insulin following an intense workout, Hertzler said, as insulin helps muscles efficiently use glucose. As expected chicken drastically lowered insulin levels, since chicken lacks carbohydrate.

The high insulin response caused by eating the moderate-carbohydrate bar was the most surprising, Hertzler continued, adding that it might not be carbohydrates alone that raised insulin levels.

"Carbohydrate and protein might work together to raise insulin levels,"​ he said. "Sports nutritionists think that an athlete who eats a combination of carbohydrate and protein after a workout might be better off than consuming either nutrient by itself.​

"Eating carbohydrate and protein together causes an insulin response that favours the replacement of carbohydrate stores in muscles and in muscle protein repair immediately after exercise. However, high insulin levels also impair the ability to burn fat, an effect that dieters don't want."​

Commenting on low-carbohydrate diet plans Hertzler concluded: "If you're on one of these diets and eat the right amount of calories necessary for weight loss, your insulin levels might be lowered, but someone following a diet high in carbohydrate and low in fat can lose weight, too."​

Full details of the study appear in the February issue of the journal Medical Science Monitor​.