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Food And Physical Activity: Sculptors Of Body Composition

What causes rapid changes in body weight?

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.


If a person does not eat for an entire day, they can wake up the next day seeing 1-2 lb weight loss on the scale. However, much of the weight loss may be attributable to water loss because of the reduction in liver glycogen and associated water. Plus the reduction in food intake can lead to reduced water coming into the body in food and beverages which would not offset urinary 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.


What causes slower changes in body weight and composition?

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. Excessive consumption of calories in the form of carbohydrate will reduce the contribution made by fat to total energy expenditure leading to accumulation. Meanwhile overconsumption of fat calories will tend to have a similar end result in increasing body fat levels. The primary reason is that body fat is the principal way that we store excessive calories. And because fat stores (adipose tissue) are low in water, body composition changes reflect a less lean body in a corresponding manner.


However, if you exercise, especially resistance exercise during excessive calorie consumption then a gain of lean body mass (fat free mass) as part of the total weight gain can be assessed. The key to maximizing the gain of leaner tissue, mostly muscle, is to eat more of the excessive calories as protein and train hard. This is what many bodybuilders do after competitions and strength/power athletes like football players do in the off season. 


When we gain weight, is it all fat?

For generally inactive people who are simply eating too much, 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 lb (~ ½ to 1 kg). 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?

In general yes when you are talking about excess daily calories coming from carbohydrate and fat and lesser degree if more of the calories come from protein. This is particularly true for inactive people who are simply eating too many calories. Even though the conversion of excess glucose to fat is not a simple process the difference in accumulate body weight and composition changes would still be nominal for most people. Here again the most important factor in weight gain is going to be the level of total calorie intake as it exceed expenditure. As carbohydrate intake increases it simply reduces the contribution made by fat toward daily energy expenditure leading the increased body fat over time.


Are energy nutrient ratios important in weight loss?

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 more of our energy expenditure will be carbohydrate. This is mostly due to the ability of insulin to promote the use of glucose for energy. Meanwhile if we eat half of our calories as protein, then roughly half of our daily energy expenditure will be from protein. Meanwhile, if you switch to a high fat/low carbohydrate diet it will take a few days to fully optimize fat burning, 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. Meanwhile as calorie level goes down, protein should make a greater percentage contribution to help limit the amount of muscle mass loss. Furthermore, resistance exercise like weight lifting can help minimize muscle losses as well.


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.


Protein in general is a critical consideration as protein helps to body hold onto muscle during weight loss. The key is to get enough protein throughout the day and at meals. Target at least 20-30 grams of high quality protein at meals beginning as early as possible and including the evening.


Furthermore, certain types of unsaturated fat can play additional roles in influencing 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.


What happens when we completely restrict calories to lose weight for a day or two?

If we completely fast for a day or two, weight loss would certainly be rapid and this fact is encouraging for “crash dieters.” However, the composition of the weight loss may not be as expected. As much as 60 to 70 percent of that weight loss might be attributable to water loss. Meanwhile, much of the remaining weight loss would be carbohydrate, and to a lesser degree, fat and protein.


Keep in mind that glycogen stores bind water. As mentioned earlier, scientists estimate that every gram of glycogen sponges about three grams of water. So during that fasting period when liver glycogen is broken down for energy, water will move out of liver cells into our blood, circulate to our kidneys, and be urinated out. This process makes the scale go down rapidly as the loss of a ½ of glycogen would lead to about 2 lbs of total weight loss.


What happens if we continue to fast for longer periods?

As the fast continues beyond a day or two, liver glycogen is no longer a major energy storage resource. Body fat breakdown is in high gear and becomes the major fuel source. Keep in mind that because all cells in the body have at least a minimal need for glucose at all times, our liver will need to generate some glucose. Amino acids become the major resource for this process. Most of the amino acids will be derived from skeletal muscle protein at first. Thus, with severe energy restriction you can certainly count on burning body fat, but you will also lose body protein (i.e., muscle mass). This is usually not what we want!


How much body protein would we lose during fasting?

Even though your body would be fueled mostly by fat during prolonged fasting, protein would still make a remarkable contribution to your weight loss. The reason lies in the energy density differences between fat and protein. Consider this example: if a man has been fasting for five days, on the fifth day he might be deriving about 75 percent of his energy from body fat and the remainder from protein. If he expended 2,000 calories that day, then 1,500 calories would have come from fat and 500 calories from body protein. If we calculate the mass (weight) of the fat and protein used it would be roughly 165 grams of fat and 125 grams of protein. That’s roughly ⅓ lb of fat and a ¼ lb of protein. Some weight loss from water would be expected due to its association to lost protein. For instance, muscle is 22% protein and 73% water. So for every gram of muscle protein lost roughly 3 grams of water is lost too.


What are ketone bodies and when do they become more important?

If starvation were to endure for even longer, less body protein would be broken down on a daily basis and used as energy. This happens for a couple of reasons. First, our brain would require lesser amounts of glucose as it adapts to use more ketone bodies. Ketone bodies are made in our liver during periods of high fat utilization. This is a survival mechanism serving to reduce the rate of loss of body protein.


During prolonged starvation, the cause of death is usually related to body protein loss. Amazingly, our brain can replace about half of its glucose requirement with ketone bodies after a week or so of complete starvation. Second, during prolonged energy restriction the thyroid gland may release less and less thyroid hormone. This slows our RMR and in turn decreases the requirement for protein breakdown. Ketone bodies might also help reduce appetite which is helpful during periods of limited food availability.


Can we lose only fat during weight loss?

When body weight is reduced, we must expect some obligatory loss in protein, water, and minerals. This only makes sense because these nutrients were important to a person before the weight loss. Even though fat tissue is composed of about 86 percent fat, when fat cells expand more of the other nutrients are needed to support the new size and metabolism of the larger cells and tissue. For instance, cell membranes of fat cells must expand and more enzymes may be needed. Furthermore, new fat cells may have been made during the accumulation of body fat. On the contrary, when fat is mobilized from fat cells, these cells shrink, thereby decreasing the need for the extra supporting nutrients. Also, when the body was heavier, the amount of skeletal muscle and density of the bones may have been a little greater to support and move the larger body. Researchers usually find that heavier people have denser bones. Thus, as body weight decreases, it is only reasonable that these areas will decrease as well. Excessive skin and some connective tissue would be broken down during weight loss as well; both of these tissues are protein rich.


If you incorporate resistance training in your efforts to change your body composition, and eat a higher percentage of calories from protein it certainly is possible to lose primarily body fat. Here, the maintenance of body protein, minerals, and water may be necessary as you enhance your muscle mass. In fact, it is possible that you might not even lose weight as you lose body fat. This might be indicative for people who are slightly overweight compared to those who are obese.

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