The heated debate, within diet circles, that began a few years ago and continues today is over effectiveness of high-protein, low-carbohydrate, type diet versus its counterpart, high-carbohydrate, low-fat diet.
To delight of Atkins diet enthusiasts, recent studies have suggested that a diet high in protein and low in fat has a greater effect on diet induced thermogenesis (calorie burning) than a high carbohydrate low fat diet.
Before we go further we need to familiarize you with a few terms we will be discussing in this article. Your total daily energy expenditure (TDEE) is total energy your body burns in a day. TDEE consists of 3 components: diet induced thermogenesis (DIT), basal metabolism, and physical activity.
DIT is increase in body’s temperature that is caused by digestion and absorption of a meal. This rise in temperature results in calorie burning. Yes, we actually burn calories simply by eating and scientists have long believed that DIT may be a factor, in reducing obesity; and that obese people may have defective DITs - although this hasn’t been proven yet. Once scientists identify link between DIT and obesity on a molecular level, it could essentially pave way for development of drugs in treatment of obesity. That’s still however, in future.
In a recent study at University of Arizona, published by American College of Nutrition, a group of young healthy women were given 2 sets of diets. (1) One diet was high in protein and low in fat and other was high in carbohydrate and low in fat. Scientists were trying to compare thermic effect (DIT) of protein versus carbohydrate during digestion and absorption of meals. Keep in mind, as body’s temperature increases (by DIT), so does number of burned calories.
Evidence from this study showed that postprandial (following a meal) thermogenesis increased 100% more with high-protein low-fat diet versus high-carb low-fat diet. Although protein had a greater effect on DIT, study did not evaluate weight loss or long term effects of this type of diet. The results did suggest that this type of diet may have a positive effect on weight loss.
Scientists concluded that a diet high in protein, moderate in carbohydrate and low in fat contents may promote a higher rate of weight loss compared to high carbohydrate, low fat diet. On other hand, they also warn that high protein diets may affect kidney function in those that have kidney conditions, but not in healthy individuals.
Furthermore, they recommend daily protein intake should not exceed 2 grams per 1 kilogram of body weight. The American daily average is 1 gram per 1 kilogram. Further studies are required to assess long term effects of high protein, low fat dieting.
It is important to keep in mind, however, that DIT or thermic effect of a meal only represents 3-10% of total daily energy expenditure (TDEE). So we must keep things in perspective. Basal or resting metabolism accounts for up to 70% of TDEE and energy expenditure from exercise is responsible for rest. Logic dictates, therefore that these two take precedence over DIT.
The other big influencing factor in weight loss is reduction of daily food intake. Let’s look at input/output equation: x (Input) – y (Output) = z. Daily output and total daily energy expenditure (TDEE) are same thing. If you ate fewer calories (x) than your body burned (y), z would have a negative value. If you consumed more calories than your body expended, z would be positive. A negative balance in equation results in weight loss, a positive value causes weight gain. It’s that simple.
In above study, high protein low fat type diet involves 2 factors of Input: Food composition and food quantity. In this diet, food composition (food selection) consists of a certain combination of macronutrients (high protein, low fat). Food intake (Input) affects DIT which causes a certain increase (energy expenditure) on Output part of equation. And, as food composition varies so does DIT. Food composition, though, can only have a limited effect on DIT. Remember DIT only represents 3-10% of TDEE (Output). And food composition (high-protein, low-fat), accounts for a percentage of DIT, which represents even a smaller value. Food quantity, on other hand, can have a tremendous effect on equation – as it increases, balance becomes more positive. If it surpasses TDEE then you gain weight - quite independently of DIT.
As a result, there can be a downside with respect to DIT involving high-protein low-fat diet or any diet for that matter. With this diet, as protein intake increases so does DIT. The problem is, however, that food quantity (Input) also increases. The point here is that there is a limit to amount of protein you can ingest before your body starts storing it as fat. Because DIT doesn’t account for expending a lot of calories (3-10% of TDEE), and food composition (high-protein, low-fat) accounts for a percentage of DIT, there’s only so much protein you can ingest before you start getting a surplus of calories. And excess dietary protein just as excess carbohydrate or fat is stored as fat in body’s adipose tissue. The only other factor that can compensate for excess of protein intake is an increase in exercise participation. Although, that would defeat purpose for obvious reasons.
Physical activity, however, can have a large effect on Output part on TDEE (Output). Not only does it account for a much larger energy expenditure than DIT, countless of studies have shown that regular physical activity actually increases basal metabolism, which accounts for up to 70% of TDEE. As a result, regular exercise participation essentially has a compounding effect on calorie burning process.
As we can see then, bulk of weight loss and weight gain comes down to quantity of calories ingested (Input) and calories burned (output). Furthermore, exercise and metabolism are responsible for approximately 90%-97% of TDEE. Energy expenditure from DIT is almost insignificant in comparison. DIT is just not effective enough to produce a negative caloric balance independently of total caloric intake, energy expenditure from exercise and basal metabolism - especially for most overweight individuals. And it would be unrealistic for overweight or obese people to rely exclusively on DIT to lose weight. These people are either overeating, aren’t active enough or have low basal metabolic rates - or a combination of all three factors.
So, it still looks like there’s no easy way out – you actually have to work, if you you’re going to lose weight. The easiest way to achieve that is with efficient use of all Input and Output components. That also means you must know your priorities. Most of your efforts should be spent in finding an adequate balance between a reduction of total daily caloric intake and a sufficient level of physical activity. And emphasis on DIT should take on a secondary role.