What I Found
Ok, guys, here goes!
Looking at diet and exercise as pertains to fat loss, there is tons of misinformation out there. The number of fad diets, gimmicks and latest and greatest secrets are staggering. Funny thing is, though, most of the factoids and myths have a grain of truth to them--problem is, that grain of truth becomes incredibly stretched and distorted, all for the almighty buck.
First factoid and the truth behind it: Protein won't make you fat. Wrong. Any calories consumed in excess of what you expend will be stored as fat. Grain of truth here is that protein requires the expenditure of approximately 25-40% of its caloric value for digestion and storage. This is known as the thermic effect of food. What this means is that if you consume 100 calories of protein, between 25 and 40 of those calories will be burned in the digestion and storage process. Compared to the thermic effect of carbohydrates (8%) and the thermic effect of fat (3%), a very significant portion of the caloric content of protein is expended in digestion and storage. So, there is a grain of truth to the "protein won't make you fat" statement--to a degree--a more accurate statement would be that excess calories consumed in the form of protein won't make you as fat as the same number of excess calories in the form of carbohydrates or fat, due to the net calorie value when you account for the thermic effect of each nutrient. BTW, this info combined with the fact that fat is a much more calorie dense nutrient, is where the low dietary fat = low body fat thinking came from.
The effect of blood sugar and insulin levels on body fat is the concept on which low carb diets are based. According to the low carb enthusiasts, carbohydrates are to be avoided because they increase blood sugar levels, which in turn increases insulin levels. The grain of truth here is that insulin is a hormone that promotes fat storage and blocks its use as a fuel for exercise. And, high glycemic index carbs, when eaten alone do spike blood sugar levels, leading to an insulin surge. But to assume that eating carbs prevents the body from using fat as a fuel for exercise in people with normal insulin responses is erroneous. Once underway, exercise causes the body to release chemicals known as catecholamines. These catecholamines blunt the insulin response, which in turn opens the door for utilization of fat as a fuel for exercise.
Many of those in the low carb camps advocate exercising on an empty stomach to promote the utilization of fat as a fuel for exercise. Again, the grain of truth here is that high glycemic index carbs do cause a rapid increase in blood sugar, which does lead to an insulin surge (effectively countered by circulating catecholamines as described above in people with normal insulin responses). And, since glucose is required by the body for all sorts of things, a glycogen depleted state will cause the body to make glucose from fat and protein (called gluconeogenesis). Fallacy here is that without the presence of carbohydrates, fat cannot be burned aerobically, period. Additionally, without an adequate supply of glycogen (the storage form of glucose), the body fatigues very rapidly, resulting in shorter, less intense exercise sessions, yielding a lower caloric expenditure overall. And, what they don't tell you as far as gluconeogenesis goes is that the body will burn at least as much protein in the form of lean muscle as it will fat (more, in most cases) to make the glucose, leaving you with less body fat, but less muscle mass, which results in a decrease in metabolic rate.
Finally, the low carb enthusiasts make out insulin to be the bad guy. Granted, insulin does promote fat storage, but it also promotes muscle growth. To try to totally negate increases in insulin levels is counterproductive when the goal is improving body composition by gaining lean muscle mass as well as losing fat.
Here are a few of my own theories--first, there are people for whom a 10-14 day period on a low carb diet could be helpful. Those who have chronically high insulin levels--too high for the blunting effect of catecholamines to have much impact--may be able to get their hyperactive insulin responses back to normal by following a restricted carb diet for a short term (10-14 days). Could they achieve the same results with a solid exercise program? Without a doubt, if they are patient enough to give the program sufficient time to work. For those who aren't, the short term low carb option may provide the kick start they need to keep them motivated.
I also think that the RDA for protein is too low, especially for active people. And, it makes little sense to base protein intake on total body weight--the person who is 10% body fat and the person who is 25% body fat, both of whom weigh 150 pounds will not have the same protein requirements. Muscle requires a constant supply of protein to maintain itself--a person with a higher percentage of muscle will require more protein than another person of the same weight at a lower percentage of muscle mass. IMHO, a more accurate estimate of protein requirements takes into account lean muscle mass and activity level, particularly resistance training and sprint type activities. The formulae available now just don't take these factors into consideration heavily enough.
Man, this is getting to be a book!! I'll post more on the topic later, if you aren't bored by now!
Thanks for reading!
Maribeth
