While the "calorie principle" has underpinned nutritional and weight loss advice over the last few decades, the fact is that different types of calories are "burned" differently in the body. What this means is that it's not just the amount of calories we consume, but the form that they come in that dictates the impact they have on body weight. There is evidence, for instance, that for a given calorie intake, those who eat the most fat and the least carbohydrate are the ones who lose the most weight [1,2,3].
There is another reason why weighing-up foods according to their calorie intake can fall wide of the mark when it comes to assessing their likely impact on body weight. This has to do with appetite. Two foods might have the same caloric content but have very different appetite-sating potential. Five hundred calories worth of steak and vegetables, for instance, might be more satisfying than 500 calories worth of cornflakes and milk. This clearly has implications for subsequent food intake and overall weight.
One apparent major determinant of a food's appetite sating potential is its glycemic index (which gives a measure of the speed at and extent to which a food releases sugar into the bloodstream). Basically, the higher a food's GI, the less satisfying it tends to be. Of 20 studies published between 1977 and 1999, 16 showed that low GI foods promoted the satisfaction derived from that meal and/or reduced subsequent hunger [4]. Overall, the results of the studies show that an increase in the GI by 50 percent reduces the satisfaction it gives by about 50 percent.
One of the theories about how a food's GI influences its ability to quell appetite has to do with fluctuation in blood sugar levels. This concept was tested recently in a group of overweight and obese women [5]. All the women in this study were given the same breakfast and lunch. This was supplemented with a glucose (high GI) drink. On one occasion the women consumed the glucose drink at breakfast. On another occasion, the drink was consumed in eight portions throughout the day. The women had their appetite assessed at hourly intervals during the day, as well as blood levels of both glucose and insulin.
Compared to those taking the sugar drink in eight portions throughout the day, those having it in one sitting at breakfast were more hungry four hours after breakfast and several hours after lunch. These differences appeared to be more closely linked to levels of blood glucose than insulin. The authors of this study concluded that their findings support the idea that changes in blood glucose can affect appetite.
The evidence suggests that those who want to put a natural brake on their appetite should emphasize low-GI foods in their diets. This doesn't just mean keeping a check on sugary soft drinks, of course. It also means controlling intake of many starchy carbohydrates such as bread and breakfast cereals. It is perhaps the generally high GI nature of these foods, which explains why individuals often say that if they eat these foods for breakfast, they get hungrier in the morning compared to eating nothing.
One breakfast meal that I recommend is low GI and I find it truly satisfies. It is Bircher muesli, which is a blend of oats, natural yoghurt, ground and chopped nuts, and some dried fruit. My experience is that individuals who eat this sort of wholesome fare at the start of the day tend not to find their appetite running out of control later on.
References:
1. Lean M E, et al. Weight loss with high and low carbohydrate 1200 kcal diets in free living women. European Journal of Clinical Nutrition, 1997; 51:243-248
2. Wien M A, et al. Almonds vs. complex carbohydrates in a weight reduction program. International Journal of Obesity, 2003; 27:1365-1372
3. Young CM, et al. Effect on body composition and other parameters in obese young men of carbohydrate level of reduction diet. American Journal of Clinical Nutrition, 1971; 24:290-6
4. Roberts SB. High-glycemic index foods, hunger, and obesity: is there a connection? Nutrition Review, 2000 58:163-169
5. A high-glycemic meal pattern elicited increased subjective appetite sensations in overweight and obese women. Arumugam V, et al. Appetite, 2007 25 July [Epub ahead of print].
Dr. John Briffa is a London-based doctor, author, and health writer with an interest in nutrition and natural medicine.
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