This has mutated into various forms from the South Beach Diet in California to the Dukan Diet in France, the Real Meal Revolution in South Africa and the Total Wellbeing Diet in Australia. It is not dissimilar to the paleo or Stone Age diets which shun grains and other carbs in favour of lots of meat plus vegetables, on the basis that it is what our ancestors ate.
The central idea is that, by eating lots of fat and protein, and virtually no carbs, the body’s metabolism switches from burning glucose to burning ketones and goes into a state of ‘ketosis’. Think of ketones as a back-up fuel when times are hard – it’s what we survive off when we burn our own fat in times of starvation. Since fat converts most easily into ketones, low-carb diets recommend lots of high fat meats and dairy products, despite neither being part of our ancestors diet.
There have been lots of studies that show:
- that it works for weight loss, but no better than my kind of low GL diet, which advocates a bit more protein, less and the right kind of low GL carbs
- that it works for diabetes reversal and lowering blood fats (triglycerides made from glucose)
- that it’s not the ketosis that makes the diet work, but the reduction in calories.
But longer term studies (1 year+) don’t tend to show a benefit over other less extreme low GL (glycemic load) dietary approaches.
For example, a review of 19 trials comparing low carb versus balanced diets concludes, ‘There is probably little or no difference in weight loss and changes in cardiovascular risk factors up to two years of follow-up when overweight and obese adults, with or without type 2 diabetes, are randomised to low carb diets and isoenergetic (calorie) balanced weight loss diets.’ Another trial comparing four diets – high carb, high GI foods; high carb, low GI foods; high protein, high GI foods; high protein, low GI foods – concludes:‘Both high-protein and low-GI regimens increase body fat loss, but cardiovascular risk reduction is optimised by a high-carbohydrate, low GI diet.’ My low GL diet may produce the best of both worlds, being medium carb, slightly higher protein, but low GL.
Low carb advocates say that the fact that a low-carb diet doesn’t produce more weight loss than other diets on the same calories isn’t the point – eating more fat and protein makes you fuller so you eat less. I’m sure this is true but the same can be said for low GL diets. Also, studies comparing a low GL diet with a high GL diet do show more weight loss on the same calories, as well as reporting substantial reduction in hunger. Also, this low GL approach is very effective for reversing both diabetes and cardiovascular disease. (I summarise these in my report gl-scientific-evidence.)
One of the selling points of the low carb diets, if you get past the agonising first week, which is how long it often takes to get into ketosis, is that you get rapid weight loss in the first two weeks. But much of this is false. When you starve the body of glucose you have to burn off glycogen stores (glucose plus water) and therefore rapidly lose weight as water. But, unless you are going to stay ketogenic for the rest of your life, this comes back.
Given that lots of people are on a variation of a low-carb diet precisely because it does work for weight loss and diabetes reversal (and/or they like meat), my concern is do these diets do you good in the long term?
The first thing to understand is that a low-carb diet is, by definition, low GL (glycemic load) and, generally speaking, that means you need less insulin and improve insulin sensitivity. That’s all good news since too much insulin drives up cholesterol, triglycerides and blood pressure. Even though some cardiologists protest that all this fat and cholesterol will raise cholesterol and heart disease, the evidence, and there is lots, is that high protein, high fat low carb diets don’t substantially increase cardiovascular risk, and may even improve it. The old notion that dietary cholesterol and saturated fat is a primary cause of heart disease and terribly bad for you is old and wrong.
High protein, low carb dangers?
However, the three main concerns raised about staying on this kind of diet long-term are kidney function, decreased bone mass, and cancer risk especially of the digestive tract, prostate and breast, plus the less life-threatening, but not insignificant issues of constipation and bad breath.
A review last year of 32 studies of high protein diets concludes: ‘there is currently no reasonable scientific basis in the literature to recommend protein consumption above the current RDA (a high protein diet) for healthy adults due to its potential disease risks.’ These risks are listed as (a) disorders of bone and calcium homeostasis, (b) disorders of renal function, (c) increased cancer risk, (d) disorders of liver function, and (e) precipitated progression of coronary artery disease.