Received a question regarding eating low-carb from a rugby player over on my my favorite bodybuilding forum; I’m a little out of my element here, since I don’t play rugby, but some general advice seemed in order to answer this guy’s questions.
Let’s talk about muscle metabolism briefly.
Your muscles basically operate in two modes: * Lipolysis * Glycolysys
Lipolysis is the basic process used for fat loss. Your fat cells release fatty acids (or you ingest them and they come through the walls of the small intestine), which are then broken down by the liver into glycerol and fatty acid chains called ketones or ketone bodies. Your cells absorb the ketone bodies for energy. While fat is over twice as calorie-dense as carbohydrates, it’s much tougher to liberate the energy and this metabolic pathway is slow; even absorption of ketones — which are a preferred fuel source for cells — is slow. Gluconeogenesis, another process fueled by the liver, provides glucose derived from proteins. This is one of the keys of why low-carb works: you take advantage of this slower metabolic pathway that requires more chemical reactions, thus you can eat more overall calories and still lose an equal amount of fat. Dietary fat and protein are also highly satiating, which helps the low-carb dieter too.
Glycolysis is the basic process used for carbohydrate metabolism. Your pancreas releases insulin, which binds to insulin receptors on your cells and provides, if you will, a “super highway” of energy to your cells, with the insulin receptor/insulin pairs acting as the traffic cops directing huge amounts of glucose into a cell. The cell can use the energy immediately (well, it takes mitochondria to get the job done, but let’s not complicate this), or store it with other ingredients as glycogen in organs and muscles, or store it as triglycerides if stored in a fat cell.
Whew! OK, brief biology lesson over. Sorry if it was review for you, but I think it’s useful for this discussion.
A lot of people wonder about the relative efficiency of glycolysis vs. lipolysis. The short answer is “we don’t know”. There hasn’t been enough science done to establish exact ratios, and as a matter of fact this “metabolic advantage” is a hotly-debated topic precisely because some research shows that it has a profound effect, and other research suggests such an effect doesn’t exist at all. Human trials are problematic for various reasons. Animal trials, on the other hand, demonstrate that high-fat, low-carbohydrate diets require 10%-35% more calories than calorie-restricted diets for equal fat loss while preserving muscle tissue.
That 10%-35% figure is difficult to nail down; we are not sure of the exact ratios, and once again it’s a contested area in the science right now. But I’m going to run with it for now, because it’s useful.
Back to rugby. If you’re on a strict low-carb regimen, another way of looking the fact of reduced calorie efficiency is that you’re operating at a 10%-35% energy disadvantage compared to your teammates and opponents. Your glycogen reserves will also be largely depleted, and such reserves provide the average person with enough energy for around two hours of strenuous effort. That number’s a bit fuzzy, too… after around 20 minutes of strenuous effort, your body kicks lipolysis into high gear anyway to supplement glycogen metabolism. That’s the heart of the “fat burning zone” stuff people like to discuss with cardio routines, because your body recognizes that glucose metabolism won’t be enough to get you through this strenuous exercise.
So what are your options if you want peak performance as an athlete, but you want to take advantage of the fat-stripping advantages of lipolysis in a low-carb diet? Well, for certain sports like bodybuilding, baseball, football, golf, and others where the focus is on brief, strenuous effort with rest periods between, you need do nothing. Your body will probably keep up just fine relying on protein and fat metabolism. If you keep well-hydrated and ingest some carbohydrate-laden drinks while exercising, you’re golden and your body should be able to keep up just fine.
For any sport in which the goal is just to complete the event rather than to win it (e.g. a marathon or century), you also need do very little. Pace yourself to stay out of the zone at which you deplete your energy stores; your pace will be a little slower, but your body would have been in lipolysis anyway to get you through the event. Keep ingesting carbohydrate-laden drinks during the event; marathon winners usually derive most of the calories they burn during the run while they are running from the drinks they ingest. The “carb-up” the night before such an event can actually hurt the performance of a low-carber during such a long run or cycle, and you’re better off staying with an eating pattern you know your body supports. Do make sure those sports drinks you consume during the run agree with you. Many a low-carber has been laid low during a marathon or half-marathon by explosive diarrhea because they drank an unfamiliar sports drink! Many steer clear of the carbs during marathons and do just fine on their lipolytic metabolism alone. But, of course, they aren’t really competitive; they just get it done at a pace they can sustain without that glucose superhighway working for them.
But what about sports that involve more constant and intense effort, such as basketball, rugby, and soccer(outside of the US: football)? For those, you’re going to have constant periods of running that are depleting your glycogen stores, plus bouts of strenuous effort that require maximum anaerobic effort that deplete your stored glycogen. Realize, I’m not a sports nutritionist and have no formal qualifications in this field (I’m a UNIX system administrator for a living), but I understand the science and think the following are logical conclusions:
1. Additional carbohydrates on the day of the bout preceding the event will almost certainly be useful, and used. No need to pig out on pasta here, just include more carbohydrates than those of us that have sedentary jobs where the only workout we get is in the gym.
2. Since you’ll be practicing daily, hopefully with intense effort, a generally increased level of carbohydrate is warranted day-to-day to ensure you have some glycogen available for the first twenty minutes of practice.
3. Consuming plenty of glucose-laden sports drinks during your match if you are on the field a lot probably won’t hurt your fat-loss efforts at all.
4. Creatine supplementation assists in the ATP cycle and muscular hydration. 5g per day during the season will help both build muscle and keep your energy levels higher during periods of prolonged exertion.
As always, measure, experiment, measure, adjust, repeat. I’d suggest just starting toward the high-end of the MANS program — around 50-60g of carbohydrate per day — and then evaluating your performance as you go along. Sugary sports drinks during your match will keep the insulin floodgates open for glucose metabolism, and may be all you need to keep your energy levels high throughout the contest.
Regards, Matt B.