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Another Piece of the Dieting Puzzle

Posted Oct 17 2008 9:14pm

Are you confused by the conflicting reports about low-carbohydrate vs. low-fat diets? Dieters aren’t the only ones. The researchers who design studies, even when they try to be as fair as possible, often don’t know all the variables that should be taken into account. A study recently published in the Journal of the American Medical Association (JAMA) gives us another clue as to why people respond differently to different diets.

Researchers found that people whose bodies produce relatively high levels of insulin in response to sugars lost more weight on a diet that was low in simple carbohydrates (a low-glycemic load diet). In the study, participants who produced more insulin lost almost five times as much on that type of diet, than on a low-fat regime. Those people also saw their body fat percentage decrease by 2 ½ times as much. By comparison, participants whose systems produced lower levels of insulin did about as well on either type of diet.

The study also looked at how the risk factors for heart disease were affected by the two different diets. Cholesterol and triglyceride counts were affected differently depending on which diet the participants followed. Unlike for weight loss, however, the amount of insulin produced by a person did not significantly affect the results in this area.

Rather than giving the dieters strictly controlled meals, the researchers relied on counseling and dietary guidance to help them chose the appropriate types and amounts of foods. This made the study particularly interesting, as it better replicated what a do-it-yourself dieter could expect to achieve. The study participants attended group workshops, and also received a private counseling session and 5 motivational telephone calls. These were more heavily concentrated near the beginning of the trial, which extended over a 6-month “intensive intervention period” and a 12-month follow-up.

The diet programs relied on the idea that they would make the participants feel more satisfied or satiated, and decrease their hunger. The presumptions were that the low-glycemic load diet would provide energy in an easily usable form, and the low-fat diet would provide foods that were filling and satisfying, but with more bulk and fewer calories. There was no calorie counting requirement, and the dieters were not told to go after specific nutritional targets. Instead, they were counseled on hunger and satiety cues, and told to “Eat when you are hungry, before you become famished. Stop eating when you are satisfied, before you become stuffed.” Physical exercise guidelines were also given based on common public health standards.

The low-fat diets in this study consisted of about 55% carbohydrates and 20% fats, while the low-glycemic load diet aimed for about 40% carbohydrates and 35% fats. Those on the low-fat program were told they should eat low-fat grains, vegetables, fruits, and legumes and to limit their consumption of added fats, sweets, and high-fat snacks. They were given lists of foods separated into high, medium and low fat categories, along with information and cooking demonstrations to help them prepare lower fat meals and use appropriate portions of higher fat foods.

The low-glycemic load group was advised to choose foods such as non-starchy vegetables, legumes, and temperate fruits, while avoiding high-glycemic load foods like refined grains, starchy vegetables, fruit juices, and sweets. Participants were also given guidance on selecting healthier fats, such as nuts, seeds and appropriate vegetable oils. As did the low-fat group, they received food choice lists, counseling and cooking demonstrations to encourage suitable choices and avoidance of inappropriate foods.

Overall, the final results showed that both diets were equally good for weight loss and reducing the percentage of body fat. The differences showed up only when looking at the amount of insulin a person produces in response to sugar consumption. When this was taken into consideration, those with higher than average insulin production did significantly better on the low-glycemic load diet. Such a diet, with fewer sugars, does not trigger as much insulin production.

When cardiovascular disease risk factors were checked, the amount of insulin produced did not make a significant difference. For both high and low insulin producers, those following the low-glycemic load diet had the most improvement in their HDL (high-density lipoprotein cholesterol) and triglyceride counts. On the other hand, those following the low-fat diet had the most improvement in their LDL (low density cholesterol). This is consistent with the results of other studies.

The researchers believe that the reduced levels of saturated fat in the low-fat diets could have been responsible for their better results with LDL. They speculate that if people on a low-glycemic load diet were careful about their saturated fat consumption, they would see bigger drops in their LDL concentrations, thus improving all three risk factors. In fact, another recent study found that women on a low-glycemic load diet that was high in vegetable fat and protein did reduce their risk of coronary heart disease.

So, how do you know if your body produces an above-average level of insulin? You could have a test done. For the study, insulin levels were checked 30 minutes after taking the standard 75g of oral glucose. But there may be no real advantage to having those results. If your insulin production is low to average, you will lose weight about as well on either diet. Meanwhile, the low-glycemic load diet seems to have the edge for improving cardiovascular health (provided you limit consumption of saturated fats) regardless of your insulin production. So being careful with sugar and starch intake will lead to better health for most people, with the bonus of faster weight loss for those who happen to produce higher levels of insulin.

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