(May be reprinted freely if linked to www.ExerciseCertification.com)
In recent years, carbohydrates have been labeled as nutrition ‘bad guy’ because of increases in insulin that occurs during metabolic processes. The secretion of insulin is dependent primarily upon concentration of blood glucose – an increase of blood sugar brings about an increase in secretion of insulin. Therefore, one function of insulin is to lower glucose.
Conversely, 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, excess glucose is shuttled off to muscles for storage. If muscles have reached their limit in storage capacity, and body does not require extra glucose to sustain body activities, excess converts to fat.
Also, as insulin efficiently clears blood of excess sugar, blood sugar levels oftentimes dip below normal and will produce infamous ‘sugar blues’ or a 'downer', followed by a possible craving for more sugar consumption. Lastly, while insulin levels are high or active, body will not burn fat as energy since 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 insulin ups and downs associated with high carbohydrate (sugar) consumption; and
3) High carbs in diet since they prevent us from burning body fat. Although these factors are true, extent or magnitude of their validity varies in accordance to a number of conditions, such as:
i) How active is individual?
ii) How many kcal is 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, more carbohydrate he or she should consume. Also, greater physical activity, less insulin 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 average individual’s diet to be in form of carbohydrate. Therefore, if a person is very active, 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-day’s energy needs. The ‘sugar’ requirements of nervous system (including brain, an organ that survives on nothing but sugar) for 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 remainder of his requirements, 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 form of carbohydrate, or 1,925 kcal, or 481 grams. If he were very active, 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 problem. Rather, it is 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 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 high fat/calorie intake.)
In regard to energy levels, one ‘pro-fat advocate’ recollected days when he trained for 2+ hours per day, while he consumed about 6000 kcal per day, and yet felt tired all 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 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.