Timing Carbohydrate Intake

When it comes to carbohydrate intake, timing can play a crucial role in keeping the body in a ready state when it’s time for the next workout.

The widely accepted dietary recommendation of eating frequent small meals, as opposed to eating a few widely spaced large ones, acts to regulate and minimize the amount of available circulating glucose over the 80 calorie level (the point at which the body releases insulin to deal with the situation). Since adipose (fat) tissue takes up glucose most rapidly, a simultaneous uptake of glucose will likely occur in all tissues when there is an overabundance of insulin-carried glucose. This results in adipose tissue’s immediate competition with liver and muscular needs, even when liver and muscle glycogen stores are largely depleted.

It is when carbohydrates are ingested in large quantities, and/or in the form of simple sugars, that conditions are favorable for the over-release of insulin and subsequent undesirable increased adipose tissue insulin-carried glucose uptake.

An ideal diet in terms of carbohydrate intake, therefore, would call for a consistent and controlled frequent intake of carbohydrates in such amounts, and with proper timing, as to steadily maintain the circulating glucose slightly above the 80 calorie circulatory capacity. This, in turn, stimulates the pancreas to release only the amount of insulin appropriate to provide for daily energy needs and to gradually replete any and all glucose energy stores (muscle and liver glycogen), with an insufficient amount remaining for significant adipose tissue storage. This well-timed, appropriately measured quantity of dietary carbohydrate ingestion would cause an extremely moderate and steady release of insulin.

A closely watched maintenance of blood sugar levels is generally accepted as being the foundation of healthy eating. But what are some other dietary considerations that can be practiced with the same relative goal with respect to carbohydrate ingestion?

• When ingesting a significant amount of simple sugar (100+ calories), also ingest either a moderate amount of complex carbohydrates, or even some protein; these combined nutrients will be digested into a chyme (the semifluid mass of partly digested food expelled by the stomach into the duodenum), thereby compromising the absorption rate of the otherwise unaccompanied simple sugar for its more gradual uptake into the bloodstream. This compromised rate of absorption, in turn, desirably prevents the exaggerated over-release of insulin. In simplified terms, if someone is going to eat simple sugars, it is better to eat them along with complex carbs and/or protein.

• Knowing the difference between simple and complex carbohydrates is obviously essential to regulating blood sugar. A rating system known as the “Glycemic Index” scores various foods relative to their unaccompanied absorption rate into the bloodstream, on a scale of 0 to 100. The higher the score, the faster its absorption rate.

• Providing carbohydrates to the body when it needs them and learning how much the body needs, relative to the hour of day and activity performed. These considerations will ideally minimize adipose tissue glucose uptake (aka fat storage).

Carbohydrates & Time-of-Day

It is important to keep in mind, after waking, that the liver has been releasing glucose energy throughout the night and is likely low on stored glycogen. Likewise, blood glucose levels will likely be low. This means that from 300-500 calories of ingested simple and complex carbs at breakfast will likely be put to good use to replenish these stores — breaking the fast, indeed. Breakfast really is the meal of the day that could arguably consist of the most carbohydrates with the intention of discouraging fat accumulation. As the day continues, in the absence of exercise consideration, carbohydrate consumption should taper off up to bedtime. Then, upon waking, the carbohydrate intake cycle can start again.

Carbohydrates & Activity

Generally speaking, glucose reserves for aerobic activity come more so from the liver than from the muscle tissues, especially once “steady state” has been achieved. Complex carbohydrate ingestion should be relatively substantial 2-3 hours prior to the performance of aerobic activity to ensure all glycogen stores are full upon initiating the exercise. It has been recommended to ingest complex carbohydrates during aerobic activity that is prolonged (60+ minutes). While this practice is still beneficial, it has since been determined that proteins are the preferred fuel of choice during prolonged aerobic activity, since the amino acid deamination process requires more time, and the resulting insulin release is more gradual and sustained. This amounts to the fact that the blood sugar level remains intact for longer periods when ingesting proteins and/or complex carbohydrates during prolonged aerobic activity.

After a typical aerobic exercise session (20-60 minutes), there is not as great a need to replace carbohydrates, as the chief energy source for the performance of aerobic activity is fatty acids. In contrast to almost every other aspect of aerobic activity, glucose stores used for anaerobic or resistance activity are substantial. These reserves are chiefly exhausted from the working muscles. For this reason, as long as the muscle glycogen stores are replenished through recovery from recent strenuous activity, there is little need to make a conscious effort to ingest a significant measure of complex carbohydrates prior to a resistance training session. In fact, it should be noted that any food undergoing the process of digestion upon the initiation of resistance training, or any strenuous activity, may rob the muscles of energy and oxygen rich blood. Blood is needed in and around the intestinal region during digestion, and therefore will not entirely be available to the working muscles to provide the much-needed oxygen.

If a significant amount of food is present in digestion, nausea and dizziness will bring a quick end to any strenuous exercise session. Also, contrary to the situation in aerobic exercise, the post-resistance workout meal should be rich in complex carbohydrates in an effort to replace, as quickly as possible, depleted muscle energy stores. This will spare intercellular proteins, and hasten the desirable metabolic shift to anabolism. Meals following aerobic exercise sessions require comparatively moderate carbohydrate and total caloric intake since the main source of aerobic energy is fatty acids.

References:

1. Burke, Louise M., Bente Kiens, and John L. Ivy. “Carbohydrates and fat for training and recovery.” Journal of Sports Sciences 22.1 (2004): 15-30

4. The National Federation of Professional Trainers. Sports Nutrition Manual. 2nd Ed. Lafayette, IN: NFPT, 2006