This question came from one of our subscribers:
The role of insulin in weight loss is well understood. However, if a person is already healthy, trim, and muscular, why should they avoid carbohydrates? Some exercise experts even advise carbohydrates to enhance workouts. What are the upsides/downsides of a low-carb approach if weight loss isn’t a goal?
Short answer: They don’t have to.
Long answer: Assuming that a person is healthy, trim and muscular, it will be a matter of careful self-monitoring to understand what level of carbohydrate (CHO) intake is right for them. Some level of CHO restriction may be necessary to maintain a certain look, but a different level may be needed for athletic performance. So, a prioritized balance will need to be worked out and, most likely, constantly tweaked.
Much of the research on fat adaptation and sports performance has been poorly undertaken, in my opinion. Phinney dived into this topic in good detail in Nutrition and Metabolism in 2004. At that time, most of the research performed on endurance training while fat adapted (and including a CHO load prior to testing) allowed no longer than 2 weeks for fat adaptation, most less than 7 days. Since the time of Phinney’s article, there seems to have been more of the same.
Much more well-designed study of fat adaptation’s effects on exercise is needed, by researchers who understand or appreciate the time needed for fat adaption is likely more than a few days. Some plans, like Rob Fagin’s Natural Hormonal Enhancement and Dr. DiPasquale’s Anabolic Solution advocate fat-adapted states with intermittent CHO loading. The anecdotal reports from followers of these plans are not enough, but could give the research community a point in the right direction.
There are cultures who eat almost no CHO and are generally healthy, and also cultures who eat high amounts of CHO and are also healthy. So, CHO intake may not be a deciding factor in the health of an individual. Instead, the quality of the food eaten, almost regardless of macronutrient content, may have stronger implications for health.
There are plenty of anecdotal cases of people feeling better on low-carb diets than high carb, and just as many cases where people feel better after adding CHO back into their diet after a low-carb approach. Research is mixed on whether or not low-carb diets affect cognition in a negative way. (Brinkworth) So, it really all comes down to personal preference with no real solid evidence that either low or high CHO diets are better for the healthy person.
Phinney SD. Ketogenic Diets and Physical Performance. Nutr & Metab. 2004;1(2)
Brinkworth GD, Buckley JD, Noakes M, Clifton PM, Wilson CJ. Long-term Effects of a Very Low-Carbohydrate Diet
and a Low-Fat Diet on Mood and Cognitive Function. Arch Intern Med.2009;169(20):1873-80.