| Originally Posted by How many carbohydrates do you need?
Introduction: This is an excerpt/section from the never to be completed opus, I had posted it to my forum and someone suggested I make it the new article of the month. If it seems a little bit incomplete, that’s because it is, apparently I never quite finished the entire chapter. In any event, this one section deals simply with the issue of how many carbohydrates you need per day.
Arguments over recommended carbohydrate intake have a long history and it doesn’t appear to be close to ending any time soon. Typical mainstream recommendations have carbohydrates contributing 50% or more of total calories while many low-carbohydrate advocates suggest far fewer (ranging from the 40% of the Zone diet to close to zero for ketogenic diets). I should mention again that percentages can be fundamentally misleading; putting carbohydrate recommendations in terms of grams per kilogram or per pound is generally more valid (with one exception noted below). A typical ketogenic/low-carbohydrate diet might contain 1 gram/kilogram (about 0.5 g/lb) of carbohydrate. An average Zone diet might contain 1 g/lb (~2 g/kg) of carbohydrate or slightly more. Typical recommendations for endurance athletes are in the 6-8 g/kg (3-4 g/lb) range and carb-loading may require 10-16 g/kg (5-8 g/lb) of carbohydrate.
Still, whether you’re looking at carb recommendations in terms of percentages of g/lb (g/kg), there is still a huge discrepancy between different experts. Some recommend lots of carbs, some recommend medium amounts, some recommend almost none.
Who’s right? In answering this question, I’m going to look at a few issues. So you know, what I’ll end up concluding is that how many carbohydrates you need (or should consume) daily depends on the same factors that affect other nutrient recommendations: goals, preferences, types and amounts of activity, and our old friend, genetic variation. By the end of the discussion, I plan to have set both minimum and maximum intake values depending on different conditions that might crop up. Let’s start with minimum amounts.
As I discussed in great detail previously, there is no actual physiological requirement for dietary carbohydrate. Most tissues can use fatty acids, the few that utilize glucose exclusively just reuse the same amounts over and over, and the brain switches to using ketones when glucose isn’t available with the body making what little is required from other sources. From the standpoint of survival, the minimum amount of carbohydrates that are required in a diet is zero grams.
Of course, when carbohydrates are restricted completely, the body has to find something to make glucose out of. That something is lactate and pyruvate (produced from glucose metabolism), glycerol (from fat metabolism) and amino acids. It’s the amino acid use that can be problematic since they have to come from somewhere. Under conditions of total starvation, that somewhere is generally muscle tissue; the body will readily break down protein to scavenge the amino acids it needs to produce glucose. In doing so, the muscle released alanine and glutamine (produced in the muscle from the breakdown of leucine and the branch chained amino acids, so you know) which can be converted to glucose in the liver.
Protein losses during total starvation are extremely high to start, gradually decreasing as the brain switches over to using ketones for fuel. Even so, in complete starvation there is always some loss of body protein. Over long periods of time, this goes from harmful (because function is compromised from muscle loss) to downright fatal.
From a body recomposition point of view, it should be obvious that losing muscle protein this way is bad. Researchers found years ago that providing adequate dietary protein helped to decrease if not outright eliminate the utilization of body protein for gluconeogenesis (a big word meaning the production of new glucose). Diets providing nothing but small amounts of protein (to the tune of 1.5 g/kg lean body mass or so) helped to almost eliminate the nitrogen losses inherent to starvation.
Recall from the chapter on liver metabolism that over half of all ingested amino acids are broken down in the liver in the first place. A good portion of those can be used to make glucose. Recent research has suggested that high leucine intakes (5-10 grams/day) may be beneficial in providing a source for glucose production in the liver.
Bodybuilders have typically used this approach while dieting, jacking up protein in hopes that it will limit muscle loss. Unfortunately, this is only successful when protein intake is insufficient in the first place. The breakdown of muscle protein is as much hormonally controlled by low insulin, falling testosterone, high cortisol and catecholamines as by nutrient availability. All of the protein in the world won’t help when your hormones are putting your body in an inherently catabolic state.
However, there is an alternate way to limit the use of body protein when carbohydrates are being severely restricted. As few as 15 grams of carbohydrates per day has been shown to limit nitrogen loss and 50 grams of carbohydrate per day severely limits the need for the body to use amino acids for gluoconeogenesis. Not only will it maintain blood glucose and insulin at a slightly higher level (thus inhibiting cortisol release), it directly provides glucose for the brain, limiting the need to break down protein in the first place.
Ketosis (if desired) will generally still develop under those conditions. So although the physiological requirement for dietary carbohydrates is zero, we might set a practical minimum (in terms of preventing excessive body protein loss) at 50 grams per day. I realize that most ketogenic diet authors use 30 grams/day as a starting point but, frankly, I have no idea where that value came from.
However, not everyone functions well in ketosis. They get brain fuzzed, lethargic and just generally feel like warmed over ****. Even with weeks of being on a ketogenic diet, they never seem to adapt completely. That’s not a good recipe for long-term adherence to a diet or healthy functioning. So we ask how many carbs it takes to avoid the development of ketosis. In general, assuming zero or very low levels of activity, an intake of 100 grams of carbohydrates per day will prevent the development of ketosis, just providing the brain with enough carbohydrates to function ‘normally’. So, for folks who want (or need) to just avoid ketosis, 100 grams per day will act as a practical limit.
Summing up so far, we’ve set a practical minimum of 50-100 grams of carbohydrates per day depending on whether or not you function well in ketosis. I want to mention again that this shouldn’t be taken as a recommendation that such an amount is ideal; it simply represents a minimum intake value.
So far I haven’t considered the impact of activity on all of this as this will drastically change the numbers above. And so you know, the values above don’t change significantly with body size. Mainly, in the above discussion we’re dealing with the brain and its glucose requirements. For the most part, brain size doesn’t scale with body weight (no jokes about athletes and the size of their brains, please); neither do glucose requirements.
So now we have to consider activity in the calculations of what might be a practical minimum (note: minimum should not be taken as synonymous with optimum). Both the type, amount and intensity of activity will impact on carbohydrate requirements. Typical low intensity aerobic/cardiovascular work doesn’t generally use a lot of carbohydrate. So if someone were only performing that type of activity (i.e. walking 3-5 times per week), there wouldn’t be any real need to increase carbohydrate intake over the above minimum. Such a person might want to increase carbs for various reasons, but there wouldn’t be any strict need to do so.
The carbohydrate requirements for weight training actually aren’t that great. I did some calculations in my first book and concluded that, for every 2 work sets or so, you’ll need 5 grams of carbohydrates to replenish the glycogen used. So if you did a workout containing 24 work sets, you’d only need about 60 extra grams (24 sets * 5 grams/2 sets = 60 grams) of carbohydrate to replace the glycogen used. So if you were starting at the bare minimum of 50 grams per day and were doing roughly 24 sets/workout, you’d need to consume an additional 60 grams (total 110 grams/day) to cover it. If you didn’t function well in ketosis and were starting at the 100 g/day, you’d increase to 160 g/day. If you don’t feel like doing such calculations, an intake of 1 g/lb or ~2 grams/kg lean body mass can probably be considered a practical minimum (an exception is various cyclical ketogenic diets which I’ll discuss in a later chapter).
I should mention that most bodybuilding experts recommend intakes in this range: anywhere from 1 g/lb on fat loss diets to 3 g/lb for mass gains so we’re definitely in that range. General recommendations for strength athletes by the nutrition mainstream are in the range of 5-7 g/kg or 2.2-3 g/lb so these values are all pretty consistent.
Higher intensity cardiovascular exercise is a little bit harder to pinpoint in terms of carbohydrate requirements. At high exercise intensities (usually sustainable only by highly trained athletes), muscle glycogen can be depleted within 2 hours or so and this can represent 300-400 grams of total carbohydrate or so. Under less extreme circumstances, carbohydrate requirements won’t be as high. And while current recommendations for endurance athletes are in the 7-10 g/kg (3-4.5 g/lb) range, studies show that most athletes consume closer to 5 g/kg (2.2 g/lb).
Frankly, if competition athletes are getting sufficient carbohydrate intake at that level, I see little reason for the average individual to consume more. I should note that the above sections assume that maintenance of muscle glycogen is the goal. Under some situations, glycogen depletion is the goal. This means that an athlete or dieter may deliberately under consume carbohydrates such that, over some time period, glycogen concentrations decline. Under others, the goal is to increase muscle glycogen above normal levels and, obviously, this will require higher carbohydrate intakes than the values above.
Ok, so we’ve looked at some minimums, what about maximum intake levels? A practical limit for carbohydrate
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03-10-2008, 07:50 PM
