In recent years, carbohydrates have been labeled as the nutrition bad guy because of the increases in insulin that occurs during metabolic processes. The secretion of insulin is dependent primarily upon the concentration of blood glucose an increase of blood sugar brings about an increase in the secretion of insulin. Therefore, one function of insulin is to lower glucose.
Conversely, the body increases blood glucose levels by secreting another hormone called glucagon.
If blood glucose levels remain high, and that energy source is not burned shortly after it is consumed, the excess glucose is shuttled off to the muscles for storage. If the muscles have reached their limit in storage capacity, and the body does not require extra glucose to sustain body activities, the excess converts to fat.
Also, as insulin efficiently clears the blood of excess sugar, blood sugar levels oftentimes dip below normal and will produce the infamous sugar blues or a ‘downer’, followed by a possible craving for more sugar consumption. Lastly, while insulin levels are high or active, the body will not burn fat as energy since the body is attempting to utilize as much blood sugar as possible. (Note that fat is not used as a primary energy source while eating an energy-sufficient, healthy diet and fat is used more heavily only during periods of fasting and extensive aerobic-type exercise.) Hence, high-fat-low-carb advocates claim that we should not want:
1) Excess carbs to turn into fat (what do they think happens to excess fat and protein kcal?);
2) To feel groggy with low energy from the insulin ups and downs associated with high carbohydrate (sugar) consumption; and
3) High carbs in the diet since they prevent us from burning body fat.
Although these factors are true, the extent or magnitude of their validity varies in accordance to a number of conditions, such as:
i) How active is the individual?
ii) How many kcal is the individual ingesting (including carbs) per meal?
iii) What comprises an individual’s food and carbohydrate intake?
HOW ACTIVE ARE YOU?
The more active a person, the more carbohydrate he or she should consume. Also, the greater the physical activity, the less insulin the body produces since muscles become insulin sensitive after exercise and glucose tolerance improves as a result. The Food Guide/Pyramid recommends about 50% of kcal in the average individuals diet to be in the form of carbohydrate. Therefore, if a person is very active, the amount should be increased to about 60% since nearly every activity uses a great deal of blood glucose and muscle glycogen for energy, but only a smaller percentage of fat. In fact, athletes who consume a high-carb diet (60%) can maintain higher-intensity exercise longer than those following a low-carb diet (<40%). If a person is relatively sedentary, then much less energy is required, and 30-40% will suffice.
The bloodstream holds about only a one-hour supply of glucose and muscles store about only a half-days energy needs. The sugar requirements of the nervous system (including the brain, an organ that survives on nothing but sugar) for the average adult is approximately 100-150 g per day (and 100 g minimum to prevent ketosis, or 600 kcal). If a 90 kg/200 pound, moderately active man consumes 3,500 kcalories per day, this is equal to 17% of his total caloric intake... just for his nervous system. This does not take into account the remainder of his requirements, the energy required for metabolism of food, or his general activity levels such as work, sports, weight training, reading, housework, walking, etc.
Since this man is moderately active, about 55% of his kcal should be in the form of carbohydrate, or 1,925 kcal, or 481 grams. If he were very active, the percent should probably be closer to 60%. That leaves 20% for fat intake, and 25% for protein intake.
HOW MANY KCAL ARE YOU CONSUMING?
Although national surveys indicate that we are eating less fat now than 20 years ago, we are also eating more kcal. Consequently, a reduction in fat and an increase in carbohydrates are hardly the problem. Rather, it is the total number of kcal consumed that is of vital importance in fat gain. If total caloric intake is below maintenance levels, a person will reduce fat, even if 80% are in the form of carbohydrates. (In fact, Southeast Asian diets are 80-90% carbohydrate, yet these individuals, on average, are not considered overweight but underweight. Conversely, an Inuit [Eskimo] diet is only about 15% carbohydrate intake and most are overweight because of the high fat/calorie intake.)
In regard to energy levels, one pro-fat advocate recollected the days when he trained for 2+ hours per day, while he consumed about 6000 kcal per day, and yet felt tired all the time. At under 200 lbs bodyweight, this person never considered in general how such a large quantity of food caused his insulin levels to go awry. He further attributed his depression and chronic fatigue to his state of hypoglycemia, but the American Diabetic Association has repeatedly stated that there is no evidence in connection to these symptoms, including nervous breakdowns, juvenile delinquency, and childhood behavior problems. Moreover, what most people experience after a meal is a change in blood plasma glucose concentrations and not actual hypoglycemia, which is a serious medical condition that requires medical treatment.
WHAT TYPES OF CARBS DO YOU CONSUME?
The next factor to consider is the composition of meals and dietary carbohydrate consumption. Obviously simple sugars/empty kcal that consist of concentrated sweets and that come from low nutrient (junk) foods should be limited or eaten infrequently. By reducing the concentrated and simple sugars in the diet, this change could contribute to a reduction in the risk of obesity, Type II diabetes, cancer, cardiovascular disease, and tooth decay. But it is not so simple as to suggest that simple sugars create the greatest insulin spike since the effect of food on blood glucose depends on several factors that constitute a meals total glycemic index.
First, the ratio and types of foods must be considered. Fat helps to slow digestion and absorption processes, thereby resulting in a lower and a less steep insulin spike. Hence, a food with a high glycemic index (e.g., potato) can have little effect on rising blood sugar levels if it is eaten with a high fat food (e.g., steak). Fiber tends to have an effect in keeping blood glucose levels down, and eating sucrose with whole wheat bread will not cause problems even for a diabetic. In fact, diabetics can consume up to 50% carb intake, so long as most are low on the glycemic index to keep blood glucose response to a minimum.
Refined starches (white flour and rice, cornstarch, pasta, enriched breads, and breakfast cereals) digest and absorb a little slower than simple sugars, but these foods still should be limited within the diet. Complex starchy carbohydrates, such as sweet potatoes, winter squash, yams, unrefined grains and grain products (e.g., barley, brown rice, buckwheat, oatmeal, and whole wheat products) are the preferred source of energy since they are high in fiber and digest the slowest. Slow digestion means slow glucose conversion, energy which burns/oxidizes during body functions at about the same rate at which it is produced.
Further, the process of digesting carbohydrates as a whole burns more kcal than the digestion of an equivalent amount of fat. However, even refined and whole grain starches break down to produce glucose, with the excess storing as fat tissue. Nonetheless, it is over-consumption of whole grains that results in added fat, a situation which is no different than over-consumption of healthy essential fatty acids or proteins. Hence, it is not carbohydrates that cause problems of excess fat gain, but the choice and amount of carbohydrate.
The form of the food also alters the glycemic response because of the time it takes for the food to be digested and absorbed:
Liquid quickly digested and absorbed.
Dry opposite to the liquid state, resulting in a slower rate of digestion and absorption.
Finely Ground digests and absorbs better than dry because of a larger surface area, and this causes food to break down better and faster.
Raw more difficult to digest than cooked foods; usually harder and tougher and requires more time to be broken down, digested, and absorbed.
Cooked breaks down, digests, and absorbs faster than its raw counterpart.
OTHER REASONS FOR HIGH (SUFFICIENT) CARB INTAKE
A most important complimentary aspect of carbohydrate is its protein-sparing effect. When the body is low in energy or when it is deprived of sufficient kcal, it will use its glucose stores. Once depleted, the body uses protein to manufacture glucose. Consuming sufficient carbohydrates guarantees that minimal protein in the muscles will be catabolized for energy requirements. Conversely, low carb diets accelerate protein catabolism to produce energy by more than 100% than with a moderate to high carbohydrate diet (50-60%).
High-fat advocates further suggest that if carbohydrates in the diet are limited, the body will use fat for energy. Although fat can supply most of the bodys tissues with energy, if need be, it cannot supply energy for the brain, which requires glucose. Even during fasting, fat is used last as an energy source. Neither can fat optimally supply the body with energy required for intense weight training, the main fuel source required from carbohydrates. Even with aerobic exercise, muscles cannot function effectively on fat alone, but will utilize glucose simultaneously. Moreover, as the body hurriedly breaks down fat for energy on a low carb diet, the process is often incomplete and produces by-products that the body must eliminate.
About the Author
(May be reprinted freely if linked to www.ExerciseCertification.com)
Brian D. Johnston is the Director of Education and President of the I.A.R.T. fitness certification and education institute. He has written over 12 books and is a contributor author to the Merck Medical Manual. An international lecturer, Mr. Johnston wears many hats in the fitness and health industries, and can be reached at info@ExerciseCertification.com. Visit his site at www.ExerciseCertification.com for more free articles and offers.
Written By: Brian D. Johnston
