While some doubt the benefits of controlling carbohydrate intake, the fact of the matter is that there is now abundant scientific evidence that this approach is generally effective for the purposes of weight loss, while at the same time helping to improve biochemical markers of chronic disease such as blood sugar levels and levels of blood fats such as triglycerides.
In a recent study presented at the American Diabetes Association symposium held in Chicago recently, the effects of low-carb eating were compared to a diet restricted in calories and fat in a group of elderly obese individuals suffering from type 2 diabetes [1]. The study lasted for a total of 6 months. At the end of this, the low-carbers had lost an average of 6.83 kg in weight, compared to an average of 5.16 kg in the low fat group. This difference was statistically significant.
In addition, though, those restricting carbohydrate saw decreases in their triglyceride and blood sugar (glucose) levels that were, again, statistically significant compared to the low-fat eaters.
There are sound biochemical reasons why they offer potential not just for weight loss, but other health benefits too. Key to understanding how this can be relates to the fact that many starchy carbohydrates cause quite brisk and sustained release of sugar into the bloodstream. The extent to which a food disrupts blood sugar is expressed as its glycaemic index (GI). In the World of the GI, glucose (a very fast releasing food indeed) is ascribed a value of 100. Compared to this, French bread, baked potatoes, wholemeal bread, cous cous and cornflakes have GIs of 95, 85, 70, 65 and 81 respectively.
The sky-rocketing blood sugar levels starchy carbohydrates tend to invoke will induce the pancreas to secrete copious quantities of insulin – the hormone chiefly responsible for tempering sugar levels in the bloodstream. Yet, while essential to life, insulin has the capacity to stimulate the production of fat within the body, and can also inhibit of the breakdown of fat too.
Of course the problem with many of the starchy carbs is not just their inherent tendency to disrupt the body’s biochemistry, but also that we so often eat so much of them. Scientists have begun to account for the quantity of food typically consumed by measuring what is known as its ‘glycaemic load’ (GL). Simply put, this is calculated by multiplying a food’s GI by the amount of carbohydrate to be found in a standard portion of that food. The GL therefore gives a better guide that just the GI with regard to the tendency for a food to disrupt sugar and insulin levels. Not surprisingly, bearing in mind their prominence in the diet, most starchy carbohydrates turn out to have not just high GIs, but high GLs too. Their ability to cause gluts of insulin mean that while starchy staples we are encouraged to have our fill of may not be fatty, they nonetheless have considerable capacity to be fattening.
Bearing all this in mind, it should come as no surprise that low-carb diets can be effective for those seeking to lose weight. But how do such diets compare with the more conventional low-fat approach endorsed by many doctors and dieticians? To date, six trials (included the one discussed above) have pitted low-carbohydrate against higher-carb/lower-fat regimes over the medium to long term. All six of these studies found that weight loss after 6 months was significantly greater in the low-carbohydrate group than in the low-fat group. Three of these studies lasted for a year, at which point there was no significant difference in results. However, in one of these studies the individuals failed to restrict carbohydrate intake to the extent advised, and in the other dietary compliance was not checked at all. Because of these limitations, these studies cannot be used to judge the true effectiveness of low-carb eating in the long term. In the final year-long study, carb restriction (Atkins’ diet) resulted in about twice the weight loss of lower fat regimes (Ornish and LEARN diets) [2].
In one review, the effects of several lower and higher carbohydrate diets were compared [3]. Overall, lower carbohydrate diets were found to bring about an average weight loss of 12.4 kg, compared with just 3.4 kg on the higher carbohydrate regimes.
References:
1. Radulian G, et al. The effects of low carbohydrate diet as compared with a low fat diet in elderly patients with type 2 diabetes.
2. Gardner CD, et al. Comparison of the Atkins, Zone, Ornish, and LEARN diets for change in weight and related risk factors among overweight premenopausal women: the A TO Z Weight Loss Study: a randomized trial. JAMA. 2007 Mar 7;297(9):969-77.
3. Bravata DM, et al. Efficacy and safety of low-carbohydrate diets a systematic review. JAMA 2003;289(14):1837-1850
