The heated debate, within diet circles, that began a few years ago and continues today is over the effectiveness of the high-protein, low-carbohydrate, type diet versus its counterpart, the high-carbohydrate, low-fat diet.
To the delight of the 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 the total energy your body burns in a day. TDEE consists of 3 components: diet induced thermogenesis (DIT), basal metabolism, and physical activity.
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DIT is the increase in the body's temperature that is caused by the 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 the link between DIT and obesity on a molecular level, it could essentially pave the way for the development of drugs in the treatment of obesity. That's still however, in the future.
In a recent study at the University of Arizona, published by the 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 the other was high in carbohydrate and low in fat. Scientists were trying to compare the thermic effect (DIT) of protein versus carbohydrate during the digestion and absorption of meals. Keep in mind, as the body's temperature increases (by DIT), so does the number of burned calories.
Evidence from this study showed that postprandial (following a meal) thermogenesis increased 100% more with the high-protein low-fat diet versus the high-carb low-fat diet. Although protein had a greater effect on DIT, the study did not evaluate weight loss or the 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 the high carbohydrate, low fat diet. On the 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 the long term effects of high protein, low fat dieting.
It is important to keep in mind, however, that DIT or the 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 the rest. Logic dictates, therefore that these two take precedence over DIT.
The other big influencing factor in weight loss is the reduction of daily food intake. Let's look at the input/output equation: x (Input) - y (Output) = z. Daily output and total daily energy expenditure (TDEE) are the 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 the equation results in weight loss, a positive value causes weight gain. It's that simple.
In the above study, the 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 the DIT which causes a certain increase (energy expenditure) on the Output part of the equation. And, as food composition varies so does the DIT. Food composition, though, can only have a limited effect on DIT. Remember DIT only represents 3-10% of the TDEE (Output). And food composition (high-protein, low-fat), accounts for a percentage of DIT, which represents even a smaller value. Food quantity, on the other hand, can have a tremendous effect on the equation - as it increases, the 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 the high-protein low-fat diet or any diet for that matter. With this diet, as protein intake increases so does the DIT. The problem is, however, that the food quantity (Input) also increases. The point here is that there is a limit to the 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 the body's adipose tissue. The only other factor that can compensate for the excess of protein intake is an increase in exercise participation. Although, that would defeat the purpose for obvious reasons.
Physical activity, however, can have a large effect on the 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 the calorie burning process.
As we can see then, the bulk of weight loss and weight gain comes down to the 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 the 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.
But wait, before you put on your running shoes and begin another diet plan, you might want to hear some very interesting news. There are certain cultures around the world whose diets contain just as much fat and carbohydrate (if not more) as in the American diet. Yet they are slimmer, and have much fewer occurrences of heart disease and cancer than their American counterparts.
Recent studies have shown that people in certain Mediterranean regions and in France manage to stay healthier and are less obese than those in other western countries. Let's look at the French first.
In a study by Adam Drewnowski of the University of Michigan, scientists examined the eating habits of 1,637 men and 1,576 women in America and compared them to those of 5,000 French adults. They studied their overall diets based on diversity (foods from 5 major food groups), variety (total number of foods consumed daily) and moderation (according to USDA dietary guidelines). (2)
The results were quite surprising. They found that the French ate more foods that were higher in fat, saturated fat and cholesterol than their American counterparts. The study also showed that the French diet complied with very few of the USDA dietary recommendations for eating healthy. In addition, the findings showed that 99% of French women's diets had saturated fat contents in excess of 10% of total daily calories. What's shocking is that, on average, the French are thinner and have fewer occurrences of heart disease than Americans.
The possible harmful effects of the high fat content in the French diet, however, were offset by diet diversity and variety. Drewnowski pointed out that "the low fat approach is very good but not if it comes at the expense of dietary variety."
The USDA recommends that diets should consist of a variety of foods. According to the American part of the study, just one in ten men and one in sixteen women consumed food from all five food groups (Meat, dairy products, fruits, vegetables and grains). The other thing is that the French have more active lifestyles than Americans do. Americans typically drive more, walk less and participate in more sedentary type of leisure activities.
Similarly, a Mediterranean diet study also showed that the diet was high in fat, more diverse and had greater variety than the American diet. According to research, certain Mediterranean people, particularly from the Greek island of Crete, had fewer cases of heart disease and were thinner than Americans.
The difference in this study, however, was a crucial finding that suggested food variety and diversity created a certain dietary ratio. This was a ratio between 2 types of fatty acids present in the Mediterranean diet. These fatty acids are found in plant sources and fall into 2 groups: The omega-6 and omega-3 fatty acids. You have probably heard of the multiple health benefits of these essential fatty acids many times before. They are called essential fatty acids (EFAs) because the body cannot produce them - they can only be obtained from food sources.
Although omega-6 fatty acids are essential to the diet, the omega-3 group has more significant therapeutic properties. Omega-3s contain powerful antioxidants that are known to fight against heart disease, lower blood pressure, strengthen the immune system, improve mood disorders to name a few.
The other benefit of omega-3s according to research is that they also have an amazing ability to control body fat. Omega-3s control the quantity of adipose (fat) tissue by regulating the amount of fat that goes into fat cells and the amount that is burned up for energy. (3, 4) Omega-3s have also been shown to increase fat oxidation in the body - the process by which fat is broken down and used as fuel for energy. (4) This further promotes a reduction in body weight that consists of fat mass.
According to scientists the key factor in diet composition is that the French diet and more so the Mediterranean diet consist of higher intakes of foods containing omega-3s than the American diet. In other words their diets contain a better (lower) omega-6 to omega-3 ratio than the American diet. And that's the key. One of the main reasons Americans have lower intakes of omega-3s is because of their high intake of processed food. Food processing is largely responsible for removing a lot of the omega-3 content from food.
On the other hand the French and Mediterranean diets are more abundant in whole foods, fresh fruits and vegetables. And so their intake of omega-3s is considerably higher. In addition, the people of Crete eat 10 times more fish (rich source of omega-3s) than Americans do. Other important sources of omega-3s in the Mediterranean diet were: fish, purslane (wild plant high in omega-3 content), walnuts, figs and various other unrefined carbohydrates. By the way, the most abundant source of omega-3s is found right here in North America, and that's flax seed oil.
As we can see, two different cultures manage to stay healthier and slimmer than North Americans while eating foods that contain high fat, carbohydrate and protein contents. The key differences are that their diets contain more unrefined foods; they consist of foods from all food groups and have more variety. As a result they have higher intakes of omega-3s (lower omega-6: omega-3 ratio) than other Western cultures. In addition, both these groups of people are more physically active than Americans.
Now, you can put on those sneakers and walk (or jog) to the supermarket for a new supply of fresh wholesome food.
Refernces:
1. http://www.jacn.org, "Postprandial Thermogenesis Is Increased 100% on a High-Protein, Low-Fat Diet versus a High-Carbohydrate, Low-Fat Diet in Healthy, Young Women, retrieved 10 June 2005 from http://www.jacn.org/cgi/content/full/21/1/55
2. http://www.sciencedaily.com, "Healthy diets need fat, according to new study", retrieved 22 June 2005 from http://www.sciencedaily.com/releases/1998/04/980424031929.htm
3. Parrish et al. "Dietary fish oils limit adipose tissue hypertrophy in rats." Metabolism, Mar 1990, 39(3):217-9
4. Parrish et al. "Dietary fish oils modify adipocyte structure and function." J Cell Physiology, Sep 1991, 148(3)
5. Baillie RA, et al. "Coordinate induction of peroxisomal acyl-CoA oxidase and UCP-3 by dietary fish oil: a mechanism for decreased body fat deposition." Prostaglandins Leukot Essential Fatty Acids, May 1999, 60(5-6)
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