Don Matesz has this new post up that goes directly against the “conventional wisdom” of the Paleo community, at least the likes of Mark Sisson, Kurt Harris, That Paleo Guy Jamie Scott, etc. Now clearly, Don is on a mission to show that Paleo does not equal low carb – but just because he is on a mission does not mean that he is wrong. And I believe that we in the Paleo community must be very careful not to establish our own “conventional wisdom” and try to defend it against objective evidence provided.
Having said this – I believe that Don’s arguments in this post are wrong – even though I have to admit that I am less hardcore on low carb than other Paleo people, simply because I personally do better with a certain amount of carbs.
I guess there are a number of statements that Don makes in this post and that go (to a differing extent) against the Paleo CW
- The body burns more body fat on a diet high on carbs than on a diet high on fat, both diets having the same (below maintenance) calories
- The body burns more excess energy on a diet high on carbs, whilst it stores more excess energy on a diet high on fats, both diets having the same (above maintenance) calories
- Low-carb diets tend to lead to muscle loss, as muscle protein is converted into carbs
The most important point is #1, but I will address it in the end as #2 and #3 are more easily to deal with.
Low-carb diets tend to lead to muscle loss, as muscle protein is converted into carbs (#3)
That this can happen is probably not too controversial – the controversy is rather about the extent to which this happens. Without doubt, even on a zero-carb diet the body has some fundamental need for carbs (maybe 75-100g/day, mostly for brain and nervous tissue; more for continued anaerobic efforts), and those carbs need to come from somewhere.
The only place where those can come from is from proteins via gluconeogenesys, and depending on the amount of proteins in the food, muscle protein will be used. Note that this is compounded to some extent by the fact the there is not real storage for protein other than the muscles – if glucose is needed, and there is no protein coming from the stomach, then it needs to come from the muscles.
The body burns more excess energy on a diet high on carbs, whilst it stores more excess energy on a diet high on fats, both diets having the same (above maintenance) calories (#2)
This might or might not be controversial, but I have certainly not heard it anywhere. The assertion here is essentially that there are quite a few “redundant cycles” for carbs, whilst no such thing exists for fat. This means that excess carbs are – in a well functioning metabolism at least – mainly converted into heat, and very little of them are stored. Excess fat on the other hand is always stored.
This assertion sounds logical, but of course when it comes to nutrition, many things sound logical, but are wrong nevertheless. Also one might argue that it is not desirable to consume excess calories in any case, be it from carbs or be it from fat.
The body burns more body fat on a diet high on carbs than on a diet high on fat, both diets having the same (below maintenance) calories (#1)
Now this is where the rubber hits the road. People like Mark Sisson are essentially saying “eat as much as you want, as long as it is low carb”. The unstated assumption behind it in my opinion though is that “as much as you want” is not an invitation for gluttony, but more an assertion that you wont eat more than you need (I slightly doubt this though; I have written about this here).
What Don is saying on the other hand is that in order to lose body fat you need to eat a low fat diet. The underlying reasoning here is that “energy balance” is cr+p, and that there is a separate balance for each of the macro-nutrients. To simplify: there is a certain need for each of the macronutrients, and the body balances each of them individually. So if you need 100g of fat and eat 110g, 10g are stored in your adipose tissue. Vice versa, if you eat 90g, you use 10g from your body. With carbs on the other hand Don seems to assert that this balance is slightly different, because of point #2 & #3: excess carbs are mostly burned, not stored, and a carb deficit is replenished from (muscle?) protein, not from fat.
Now intuitively I would think that this view of separate balances is a bit simplistic – after all there are healthy people across a wide spectrum of different macro-nutrient ratios, so what would that “optimum balance” be? On the other hand, he cites a study that seems to show exactly this. The key chart of this study is reproduced here:
What is seems to show is that on a “High Fat Diet” intake ~ oxidation for each of the macronutrients, ie they are all used up to energize the body (in fact, carbs are in slightly positive territory, which would indicate that the calories are slightly above maintenance and this excess is burned). On a “High CHO [carb] Diet” on the other hand the bars for fat are stongly negative (meaning body fat is used up) whilst the bars for carbs are highly positive (meaning that carbs are burned).
Now I quickly want to get one explanation out of the way: I do not understand the study well enough, but what this chart could in principle mean is that carbs are converted into fat (rather than burned in empty cycles) and that the resulting fat is then burned. I trust that the authors of the study have made sure that this explanation is false.
So this leaves us with the explanation that the fat metabolism is essentially constant (you cant see this from this chart, but Don asserts this in his post, based on other data in the study) so the less fat you eat the more body fat you burn, ie the balance-by-macronutrient hypothesis is true.
Now I am physicist, not a physician, and I do not have the knowledge to assess whether or not this particular study made sense. I hope that others better versed than myself (Jamie Scott maybe?) might chip in. The one thing I can think of though is that 7 days is not a very long period. I suppose if you have a carb-centered metabolism then it takes a tad longer than a week to convert this into a fat-centered metabolism, so in the short run what you’d see is exactly this…