Its time to show once and for all that the magic diet is a myth and that all calories from all sources such as protein, fat or carbohydrate are equal. Its simply a matter of food as a fuel and calories are the energy content of food.
A recent study published in the Journal of the American Medical Association has raised a lot of controversy as it appeared to show what could potentially be the holy grail for dieters - Calories eaten from different sources are unequal.
Could calories from a piece of bread have a different effect on your metabolism that an equivalent number of calories from an apple or a piece of chicken? This was the claim. If so it would put one diet clearly ahead of the other, namely that low calorie high protein diets are best because they don't trigger a 'starvation response'.
This means your weight loss program would be more effective on one diet than another. If you adopted a low calorie diet with low carbohydrate you would lose weight faster than on a diet rich in carbohydrate with the same overall number of calories.
Low carb diets would be the magic diets that everyone was looking for. But these findings are very controversial.
This article explores the evidence for this assertion, why it gained so much notoriety and why the claims may be wrong.
The issues relate to the raging controversy over the relative merits of low carb, low fat and high protein diets and all the other variants that are out there, such as Atkens, Dukan, Paleo and Mediterranean Diets, to name a few.
The study was based on a relatively small number of 21 people. Their food was tightly controlled. Initially they were fed on a reduced calorie diet so that they lost about 10 to 15 percent of their weight.
Such people are vulnerable to another myth that fasting and low calorie diets causes the metabolic rate to slow down, so that people can put weight back on despite eating less, or their weight loss rate declines.
The research team also measured how many calories each of these people expended daily, both in terms of their resting calorie expenditure rate and total expenditure.
This energy consumption after their weight loss, was used to set the amount of calories each individual was fed for the rest of the test.
Each of the 21 subjects were put through three very different diets, spending a month on each of them.
They consumed exactly the same number of calories on all three diets, exactly equivalent to the number of calories were consuming after their initial weight loss.
However the nutrient composition of these diets was very different.
Low-Fat Diet - This diet was low-fat, but was high in carbohydrate. It included lots of whole grains, vegetables, fruits, lean protein sources. This diet had 60% of calories from carbohydrate, 20% calories from fat, and 20% calories from protein; The carbohydrate had high glycemic load.
Low glycemic index Diet - This diet had much less total carbohydrate, which was the type that is digested and used slowly, from beans, vegetables and unprocessed foods. This diet had 40% calories from carbohydrate, 40% calories from fat, and 20% of calories from protein; the carbohydrates provided a moderate glycemic load.
High Protein and Low Carbohydrate Diet - This diet is the Atkins and Dukan model, which has carbohydrates and high levels of protein and fat (less in the Dukan Diet). This diet has 10% calories from carbohydrate, 60% calories from fat, and 30% calories from protein; the carbohydrate provided a low glycemic load.
The results from the study are shown in the images below.
There was an apparent correlation between the relative proportion of carbohydrates in the diet and energy expenditure.
The lower the carbohydrate in the diet the lower the resting and total energy expenditure.
The researchers argued that with the very low-carbohydrate and high protein Atkins diet, no metabolic rate change occurred in response to the weight loss.
Test subjects expended, on average, about 100 less calories a day than they did at their full weights.
Some 8 of the 21 subjects actually expended more calories than they did at their full weights (as shown in the images as zero on the graph).
This was the opposite of the predicted metabolic compensation for loss of weight - that is for there to be a drop in metabolic rate when dieting.
The test subjects on the low-fat and high carbohydrate diet expended and average of 300 less calories a day than they did before dieting and those on the low-glycemic-index diet expended an average of 150 less calories.
The conclusion from this is that trying to lose weight when eating a low calorie and low-fat diet with lots of carbohydrate will be harder because the body tends to lower the metabolic rate more in a so-called 'starvation' response, but that this does not occur with high protein diets. There are various studies that debunk the starvation response for short-term fasting.
The concluding comment in the paper by the authors and the stated limitations are perhaps the most controversial aspect.
These findings are very controversial and many have claimed that they are erroneous, particularly when only 21 subjects were used in the study and the test period was only for a month. Even the graphs themselves are somewhat unconvincing as there is considerable overlap in the responses of the individual subjects.
One major criticism has been whether there was due consideration for loss of water from the body being mistaken for loss of fat. High protein and low carbohydrate diets are renowned for inducing water loss. The metabolic rate measurements are usually expressed as calories expended per unit of lean body mass, that is the part of the body after excluding fat. When water is eliminated from the body, the net lean body mass goes down. This means that the calories expended per unit of lean body mass will erroneously go up. This loss of water could explain why those on high protein diets appear to have higher metabolic rates. Only more extensive research will confirm this.
Perhaps the most contentious claim from this study (as shown above) is the contention that a calorie is not a calorie, but its value depends on how much carbohydrate is in the diet. However the laws of physics are inflexible - calories consumed must exactly equal calories burnt when fat storage remains unchanged. To say otherwise does not make sense.
To lower the amount of fat stored in the body and so reduce obesity, one must generate a calorie deficit. This means that the calories taken in, must be less than the calorie burnt through normal metabolism and extra activity, that is there needs t be a deficit. This principle of conservation of energy applies whatever the source of the calories - pumpkins or peanuts, steak or cheese. To claim otherwise is to claim that one of the laws of physics has been broken. The authors conclusion applies not to the physics but to the physiological response to the diet, perhaps triggered by hormonal changes.
Dr. Rudolph Leibel, a long time obesity research scientist at Columbia University has argued strongly against this notion of the flexible calorie and refers to his own research. His team conducted an experiment with a group of people who were of average weight. They lived in the hospital and had very tightly controlled diets. They were fed liquid diets with precisely measure calories that were precisely monitored to keep their weights absolutely constant. While the calories were kept constant, they changed the proportions of carbohydrates and fats in the diets in major ways. Some subjects had virtually no carbohydrates, and some had practically no fat. The study showed that the level of fat and carbohydrate had no effect of the subjects weight which remained constant despite the changes in diet.
Dr. Rudolph Leibel advises that to lose weight people should eat a lower-calorie diet. They should eat healthily and eat what they usually eat, but eat less of it (reduce portion sizes). They should carefully measure what they eat to ensure that have a calorie deficit. The idea is to eat as little as you can tolerate, and do more exercise. There is no magic diet now or waiting to be found. There are probably nor real preferred diet, so long as the diet creates a calorie deficit? Some food compositions will suit some people more than others, Eat Less, Eat Smaller Portions, Eat Nutrient-Dense Foods - USDA Dietary Advice. It requires a lifestyle change not going on a diet for a month. Whatever diet you adopt it has to work for the longer term as the maintenance phase is the most critical. Most people who lose weight on diets, put it all back on when they resume normal eating patterns and foods.
There is a simply no healthy magical answer to obesity: Eat the foods that many thin communities around the world eat: high in vegetables, rich in complex and unprocessed carbohydrate and limited portion, rice-based diets, with small amounts of meat.