vidence suggests that highly refined carbohydrate foods are a major cause of obesity. Refining cereal grains removes the bran and the germ layers, the parts of the grain that contains most of the fibre and micronutrients. Refined carbohydrates therefore comprise mainly of the starchy endosperm, which contains energy, but few other nutrients. Because refined carbohydrates are missing their fibre, digestion speed is accelerated and the glucose within the starch can enter the blood stream more rapidly. This causes an increase glycaemic response which is thought to lead to abdominal visceral fat accumulation and insulin resistance, which are major risk factors for obesity. In the long-term, consumption of refined carbohydrates also leads to mineral deficiencies. This can worsen glycaemic control because some minerals, particularly zinc, calcium and chromium, are required for insulin function. Therefore. highly refined breakfast cereals may be detrimental to body composition by contributing to poor glycaemic control.
Researchers1 have investigated the glycaemic effects of refined breakfast cereals, by comparing the glucose and insulin responses of 11 healthy female subjects to a meal containing refined or whole grain breakfast cereal. The meal consisted of either corn flakes or all bran supplying 30 g of carbohydrate, along with 50 g egg, 133 g orange juice, 129 g milk, 180 g coffee and 5 g margarine. The all bran provided 19 g fibre, whereas the cornflakes provided only 1 g. The glycaemic index of corn flakes in 82, whereas the glycaemic index of all bran is 40. Following the breakfast the plasma glucose levels were assessed at staggered time intervals using blood samples. The corn flake meal produced plasma glucose and insulin responses that were significantly higher at 60 min compared to the all bran meal. In addition, the area under the curve for the corn flake meal was 40 % greater, when compared to the all bran meal.
These data reflect the higher glycaemic index of corn flakes, which likely results from the lower fibre content. Long-term ingestion of such refined energy dense nutrient poor foods are known to increase the risk of developing obesity and metabolic syndrome. That refined carbohydrates are detrimental to health and body composition is demonstrated in studies where elimination of refined carbohydrates has resulted in weight loss with no calorie restriction (here). Such ketogenic diets appear to work because they allow the individual to control the previously dysfunctional insulin system that resulted from consumption of refined carbohydrate foods. Similar improvements are seen with the consumption of whole grains. Whole grains are an integral part of the Mediterranean diet, and such diets have also been shown to cause weight loss without calorie restriction (here). Therefore evidence supports a role for refined carbohydrates in the development of obesity.
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