I've spent a fair amount of time thinking about the recent Internet dust up between Dr M Eades and A Colpo. Two very bright individuals with strong ego's. Each with a vested interest, for very different reasons, in the existence, or lack there of, of a metabolic advantage in very low carb ketogenic diets (VLCKD). The basic problem for each of them is that each of their arguments can be, and have been negated. There are a number of studies that categorically find that any and all weight loss is a matter of caloric balance. There are other studies that find the exact opposite. To assert that there is a universal advantage to VLCKD's, is to invite a "black swan". In other words, all it takes to negate the argument, is a single person for whom the advantage does not exist. The same holds true for the opposite argument, one person who shows a metabolic advantage on a VLCKD, negates the argument that caloric balance is all that matters.
So what are we left with? A paradox? Not quite.
Each argument assumes that the only independent variable is diet. When dealing with human beings however, things like diet do not exist in a vacuum. One of the big, if not the biggest variable in determining if someone will show a metabolic advantage with a low carb diet or not, is insulin sensitivity. If you are resistant to insulin, and/or have hyperinsulemia, then I have little doubt that carbohydrate restriction will allow you to eat more calories and still loose weight, then would be possible on a standard high carb low fat diet. Hence the existence of a metabolic advantage. If, however, you are insulin sensitive, a low carb diet will not affect your weight loss or gain beyond caloric balance. --No metabolic advantage. (In fact I've seen two studies that show that insulin sensitive people do better on low fat diets)
So what we really should be asking is how do we tell who is going to derive the most benefit from low carb diets. If you and your doctor are willing, go and have some lab work done. A standard lipid panel, A1C, and fasting glucose, would get the job done. The standard lipid panel is going to provide you with your HDL and triglyceride numbers. Ideally when you divide your triglyceride number by your HDL number it should be less than 2, 3 is ok but not great, 4 is not good, and 6 is really not good. Your fasting glucose should be less than 100, and your A1C less than 6. Depending on where you are in your progression with insulin resistance, the Tg/HDL ratio will be the first place it will show, followed in order by high fasting glucose and then elevated A1C. If your glucose is over 126,and/or your A1C is over 7, you probably have or are well on your way to diabetes, and your doctor has probably already scheduled you for more tests. If any of the following apply to you, you can benefit by cutting down on your carb intake; fasting glucose is over 95; A1C is 6 or more; TG/HDL ratio is above 2. The farther you are from these values, the more you need to cut your carbs. If you are diabetic, or very close, then you may need to down to less than 50g of carbs, if you are just a little off, then somewhere between 100 - 150g will probably do the trick.
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Paragraphs are good! :-)
This whole metabolic advantage discussion needs some clarity and precision as to the hypothesis under question. If it's that a low-carb diet can effect more fat loss with the same number of calories, that's a complicated question to address with certainty.
But if the hypothesis is that the body burns more calories under a VLCKD compared to a standard diet with the same number of calories consumed, we can make some headway. Let's start with a couple of basic points which I think everyone believes to be true:
1. Gluconeogenesis is the process where the body manufactures glucose from proteins. Gluconeogenesis requires energy. Thus, 100g of consumed glucose yields more net energy than 100g of manufactured glucose yielded by gluconeogenesis.
2. If your blood glucose drops too low, you will die. Thus, if you do not eat glucose, you need to make it via gluconeogenesis.
Now, unless there is some compensatory mechanism, whereby some other metabolic process(es) uses less energy under a VLCKD, then holding all other things constant (e.g. physical activity), more calories are spent in the VLCKD than in the standard diet.
How/if that plays into fat loss gets us back to more complex territory. If gluconeogenesis yields less net energy than direct consumption of glucose, then presumably appetite should compensate, as it likely does when more energy is expended through physical activity. But that view is probably oversimplified, as it neglects other physical effects (like hormones) that differ between the VLCKD and standard diet.
Carbohydrate restriction improves the features of Metabolic Syndrome. Metabolic Syndrome may be defined by the response to carbohydrate restriction
http://www.nutritionandmetabolism.com/content/2/1/31
Pretty much what I concluded; it's not a question of a metabolic advantage (or not), but rather, some people are intolerant of carbohydrate and these people do not have normal metabolic functions while eating such a diet. They make less energy, store more as fat, abnormally.
Insulin hypersecreters will always do better with the low carb diet (assuming their excess insulin production is corrected by reduced glucose diet). And by "better" I mean to say they burn more energy, gain less weight, exercise more, etc and generally weigh less.
Those without such vulnerabilities can eat their weight in cereal and gain little to no weight... because, for them, it all comes down to total energy of diet, or perhaps lifestyle/stress/activity as an ultimate mediator of metabolism (thus weight).
I have to side with Dr. Eades on this one. What's the best way to get rid of excess calories? Thermogenesis. As mammals, we spend the vast majority of our calories generating heat.
Carb-rich meals diminish thermogenesis in comparison to protein-rich meals. Check out this reference:
http://www.ncbi.nlm.nih.gov/pubmed/11838888?ordinalpos=21&itool=EntrezSystem2.PEntrez.Pubmed.Pubmed_ResultsPanel.Pubmed_RVDocSum
There's no denying that diet composition affects metabolic rate, even when meals are kept isocaloric.
Stephan,
The fact that a protein adequate diet will cause more weight loss then a protein poor one, is not in question. The question is if both diets are protein adequate, what is the effect of carb vs fat restriction while keeping calories equal. Generally speaking, the effect of the carb reduction is most visible in people with insulin resistance, while insulin sensitives will not show a difference beyond caloric balance.
I thought the debate over the "metabolic advantage" was simply, does anything matter for weight loss other than total calories?
In other words, does diet composition affect metabolic rate?
The "argument" is over the effect of carbohydrate restriction. It gets confused because in "real life" people who cut their carbs generally increase their protein. Drs Eades, Atkins, and others have claimed that the metabolic advantage is due to carb restriction. Under controlled conditions, its very much an individual thing, and generally related to degree of insulin resistance.
Stephan, carbohydrates can generate thermogenesis. But not the types of carbohydrates most people eat. I am thinking of fruit juices (esp raw), and maybe raw vegetable juices too. They definitely speed up metabolism at least in some people. In fact, I doubt anybody could get or stay fat on raw juices. Cooked juices aren't the same, but I'd say they're still vastly less fattening and unhealthy than refined sugar and HFCS.
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