How Many Carbs Do I Need to Spare Protein Loss?
Early research into the topic of starvation and low-carbohydrate dieting found that as few as 15 grams of carbohydrates per day can limit nitrogen loss in the body. And raising carbohydrate intake to 50 grams per day severely limits the need for the body to use amino acids for gluoconeogenesis (which is why I suggested setting daily carbs on the low-carb days of The Ultimate Diet 2.0 at 50 grams).
This occurs via at least two mechanisms:
1.The increased carb intake maintains blood glucose and insulin at a higher level (inhibiting cortisol release).
2.The carbohydrate provides glucose for the brain, limiting the need to break down body protein.
Basically, in the context of dieting, dieters can either jack up dietary protein to cover the increased carbohydrate requirements of dieting or simply eat slightly more carbohydrates to provide them directly. Both have the same end-result. 15-50 grams per day limits the body’s need to break down protein and will allow protein requirements to be set lower than a diet providing essentially zero carbohydrates per day.
But What About Ketosis?
Since I’m going to use the term in just a second, I need to define what it means. When fatty acid burning is ramped up to high levels (as when carbohydrates are restricted), the body starts producing ketone bodies in the liver. As noted above, many ues in the body can use ketones for fuel, basically they are an alternative energy source to glucose when it’s not available. When ketones build up in the bloodstream beyond a certain point, a condition called ketosis is said to develop. In contrast to the diabetic ketoacidosis (which occurs in poorly treated Type I diabetics), dietary ketosis is not dangerous and is an adaptation by the body to total starvation.
Many diets such as The Atkins Diet and other very low-carbohydrate diets are based around establishing ketosis for various reasons which are beyond the scope of this article. I only bring this up as most ketogenic diets set a carbohydrate intake level of roughly 30 grams per day (allowing some vegetables but little else) although I’ve never found support for that specific value.
I bring this up in the context of this article as many people start such diets with the specific goal of developing ketosis (again, for a variety of reasons). Since many books give the 30 g/day value for a ketogenic diet, folks get a little anxious about carb intakes that are higher than that.
However, strictly speaking, any diet with less than 100 g/day of carbohydrate will cause ketosis to develop to some degree (more ketones will be generated as carbs are lowered). I’d note that many ketogenic dieters use Ketostix to track ketosis, small sticks that measure urinary ketone levels. These are misleading for a number of reasons, not the least of which is that while ketosis (as defined by blood concentrations of ketones) may develop, urinary ketones don’t always show up, especially as carbs are raised to nearer the 100 g/day high end.
In any case, an intake of 15-50 grams per day of carbohydrate will still allow ketosis to develop and those ketogenic dieters attempting to ‘eat as few carbs as possible’ might want to consider that in the context of not only providing much needed food variety (at 50 g/day, even a small amount of fruit can often be fit in) but also in the context of the protein sparing
ues I discussed above.
Getting to the point, 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’d note again that, within the context of The Rapid Fat Loss Handbook approach, carbs are limited to essentially trace amounts; however protein (which makes up the majority of the diet) is set high enough to limit muscle loss.
However, not everyone functions well in ketosis. They get brain fuzzed, lethargic and just generally feel awful. 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 or training.
Tangentially, I’d note that this seems to be related to inherent levels of insulin sensitivity. Individuals with good insulin sensitivity, who typically run well on carbohydrates, tend to not do well on low-carbohydrate diets. In contrast, individuals with insulin resistance often do far better reducing carbohydrates and that often means going to ketogenic levels. Finally, some people seem to have the metabolic flexibility to do well with either diet. I address this
ue in more detail in article Insulin Sensitivity and Fat Loss.
So what if people want to avoid ketosis? In general, assuming zero or very low levels of activity, an intake of 100-120 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, 100-120 grams per day will act as a practical limit. Again, this won’t quite work as a recommendation for people involved in high-intensity activity since not all of the incoming carbs will be available for the brain.
So, summing up mid-article, the absolute requirement for carbohydrates is zero grams per day. However, depending on protein intake, a practical minimum for carbs lies between 50 grams/day (if someone functions well in ketosis) to 100-120 grams per day (if they don’t function well in ketosis). Let me mention very specifically that I’m not suggesting those numbers are a recommended level, I’m simply using them to represent a practical minimum value.
As a final note, before addressing the ue of exercise, I want to note that the above values above don’t change significantly with body size (e.g. it’s one of the few places that an absolute number of carbs, rather than an amount set relative to bodyweight is appropriate). Most of the above discussion deals with the carbohydrate requirements of the brain which, for the most part, doesn’t change massively with body size. A 120 pound female and a 200 pound male have roughly similar carbohydrate requirements for their brains because brain size simply doesn’t differ that much between them
.