What causes changes in body weight and composition?
Very rapid changes in body weight are usually caused by fluctuations in body water status. For instance, water losses via sweating and/or poor fluid consumption can reduce body weight by 2 lb (1 kg) for each lost liter. This mild dehydration is common as the principal prompter for fluid consumption is thirst, which you might not perceive thirst until your body weight has been reduced by about 1 percent as water. Even if a person does not eat for one day, half of the weight loss may be attributable to water loss. On the contrary, there are certainly times when we may hold a little extra water in our tissue. Women certainly know this to be true at certain points in their menstrual cycles.
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On the other hand, more significant changes in body weight and composition over time are more attributable to regular over consumption or under consumption of calories as well as type of diet we eat and exercise we perform. In general, the effects of these factors are relegated to specific hormones and other signals. The handling of energy nutrients being absorbed from the digestive tract is primarily influenced by insulin. In contrast, glucagon, cortisol, and epinephrine largely control the handling of stored body nutrients during fasting or exercise. In addition, serious exercise leads to additional signals in muscle to adapt and possibly get bigger (thus influencing body composition). |
How would weight gain from overeating affect body composition?
When we eat more energy (calories) than we use, much of it will be stored and we will gain weight. Remember, our ability to store carbohydrate (as glycogen) is limited to about 300 to 500 grams and body protein content is based upon the protein needs of our body, not how much protein we eat. This means that the more carbohydrate and protein we eat, the more we will use for energy during the hours that follow and throughout the day. This will decrease our use of fat as a fuel source. In addition, some of the energy in the carbohydrate and protein we ate will be used to make fat. So when we eat too many calories, less body and food fat is used for energy and a little fat is made as well. Subsequently, more and more body fat will accumulate over time.
When we gain weight, is it all fat?
Not all of weight gain is fat. By virtue of expanding fat cells and of simply being a larger person, the absolute amount of body protein, mineral, and water also increase. For example, if a person’s body weight increases by 10 pounds (~ 4.5 kilograms) due to overeating, the amount of protein in the body may increase by ¼ to ½ pound (~ ½ to 1 kilogram). The accumulation of non-fat, supportive substances may account for as much as 20 percent of our weight gain from chronic overeating. However, since the increase of these nonfat substances like protein is small relative to the increase in fat, their percentage of our total body weight will still decrease. Body fat percentage can climb upward of 70 percent of total body weight in morbidly obese people. This latter situation would leave only about 30 percent for all other body components.
Will different types of diets evoke the same weight gain?
The conversion of excess glucose and protein to fat is not a simple process. These substances must engage in chemical reaction pathways, which will require some energy to operate. Therefore, our body must expend energy to make fat. This means that a person eating a higher-carbohydrate/protein diet in excess of energy needs will not store quite as much energy in the form of fat in comparison to an individual who eats a high fat diet in excess of energy needs. So, to address the notion that higher-carbohydrate diets make us “fat,” the answer is yes, but only when we eat more calories than we burn and over time. However, if we eat the same amount of fat calories in excess of expenditure it is easier for our body to store the food fat as body fat.
Are energy nutrient ratios important in weight loss?
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Over the past couple of decades several popular diet programs and philosophies were founded on eliminating energy sources or creating energy nutrient ratios. The late 1970s and 1980’s seemed to be about removing fat from the diet while the last couple of decades we have seen the emergence of The Zone and re-emergence of Dr. Atkins’ Diet Revolution and the explosion of The South Beach Diet. The Zone is based on a lowered calorie intake and partitioning calories between carbohydrate, protein and fat in a 40:30:30 ratio. Meanwhile, Atkins and South Beach are based on strict carbohydrate restriction for a period of time followed by reintroduction of some carbohydrate back into the diet.
But what do we really know about energy nutrient ratios and their influence on weight loss, weight gain, and body composition? |
It does seem that when we eat carbohydrates and protein they are used for energy before fat; there is a hierarchy of food calorie utilization. For instance, if we eat 70 percent carbohydrate, then roughly 70 percent of our energy expenditure will be carbohydrate. This is mostly due to the ability of insulin to promote the use of glucose for energy. If we eat 50 percent protein, then roughly that amount of our daily energy expenditure will be from protein. Meanwhile, if you switch to a high fat diet it will take a week or more before you begin to match the higher fat intake with higher fat used for energy, but you get there.
Research studies have helped health professional understand how different types of diets can help people lose weight and improve body composition. It does seem that in the short run, up to 6 months of dieting, lower carbohydrate intakes allow for a little more weight loss than higher carbohydrate intakes. However extending out longer, both diets do about the same when it comes to weight lost and people aren’t able to “stick with” one diet better than the other. So, in general the most important nutritional factor in determining weight loss is calorie level. However as we will discuss soon determining an energy nutrient ratio is personal and will depend on several factors.
Are certain nutrients better for weight management than others?
Research studies have supported the notion that all calories are not equal when it comes to leading to body fat accumulation. For instance, all foods increase our metabolism to some degree, which scientists refer to as the Thermal Effect of Food (TEF). However, when people eat different meals containing the same number of calories but with different nutrient compositions, in some cases they burn more calories in the couple hours that follow. In particular, foods with more calories from protein and unsaturated fat tend to increase calorie burning more than if those same calories came from saturated fat. So less of the food calories would be available for fat storage.
Furthermore, certain types of unsaturated fat can play additional roles in influencing e our ability to make fat from excessive diet-derived carbohydrate and amino acids. Some studies have shown that eating a diet which derives more of its fat from good food sources of omega-3 PUFAs (e.g., fish) may actually decrease our ability to make fat from excessive diet-derived carbohydrate and amino acids. This is another good reason to eat a couple servings of fish weekly or to take a fish oil supplement.
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