Monday, January 7, 2008

A ketogenic (low carb) diet limits hunger

Low Carb

I've talked before about low carb diets. To be honest up front, I believe in low carb diets - I think they are healthier, tastier and more effective for getting you to burn fat.

ketogenic diets

Emma has a really good explanation of what a ketogenic diet is

Ketosis is a kind of soft metabolic switch, when the body burns fat primarily for fuel instead of glucose. Imagine if your car could run on both petrol and electric at the flip of a switch, and the two could be mixed to different proportions to produce different effects. Ketones are the substances produced when the body breaks down fat (dietary or body stores) for fuel in the liver. It's a dimmer switch, we all produce ketones all of the time, though those of us on a high carbohydrate Western diet don't produce very many. Our ancestors who lived during the ice ages and ate mammoth fat probably produced a lot of ketones. We usually have a higher ketone level in the morning, after an overnight fast.

The more fat we eat in relation to carbohydrate and protein, the more ketones we produce for energy, though even low-fat calorie restricted diets produce small amounts of ketones – it would be a biological impossibility to lose weight without producing them, as they are simply the by-products of all fat burning. Ketones only appear in significant amounts when insulin is lowered to a critical point. The body seems to prefer to operate either in the presence of insulin, or the presence of ketones, which bypass insulin. It does not operate more efficiently in the presence of both, as insulin suppresses ketone production. The body actually runs more efficiently on ketones than it does on insulin, as demonstrated by numerous studies available in PubMed, including the body's heart function and brain function. If you hear that ketones are "dangerous" in the media or from your doctor or nutritionist, their information is out of date and based on a misunderstanding of what diabetes is and what it does to the body.

A ketogenic diet restricts protein to the RDA amount, restricts carbohydrates to less than twenty grams, and makes the rest of the diet up with fat. This comes to 80-83% of calories from fat, about 10-13% from protein, and barely 3-5% from carbohydrate. This diet is similar to the diet recommended by the longest living type I diabetic, Dr. Richard K. Bernstein MD.

Here is a new study which says that a ketogenic diet reduced hunger in obese men:

Effects of a high-protein ketogenic diet on hunger, appetite, and weight loss in obese men feeding ad libitum 1

Background: Altering the macronutrient composition of the diet influences hunger and satiety. Studies have compared high- and low-protein diets, but there are few data on carbohydrate content and ketosis on motivation to eat and ad libitum intake.

Objective: We aimed to compare the hunger, appetite, and weight-loss responses to a high-protein, low-carbohydrate [(LC) ketogenic] and those to a high-protein, medium-carbohydrate [(MC) nonketogenic] diet in obese men feeding ad libitum.

Design: Seventeen obese men were studied in a residential trial; food was provided daily. Subjects were offered 2 high-protein (30% of energy) ad libitum diets, each for a 4-wk period—an LC (4% carbohydrate) ketogenic diet and an MC (35% carbohydrate) diet—randomized in a crossover design. Body weight was measured daily, and ketosis was monitored by analysis of plasma and urine samples. Hunger was assessed by using a computerized visual analogue system.

Results: Ad libitum energy intakes were lower with the LC diet than with the MC diet [P = 0.02; SE of the difference (SED): 0.27] at 7.25 and 7.95 MJ/d, respectively. Over the 4-wk period, hunger was significantly lower (P = 0.014; SED: 1.76) and weight loss was significantly greater (P = 0.006; SED: 0.62) with the LC diet (6.34 kg) than with the MC diet (4.35 kg). The LC diet induced ketosis with mean 3-hydroxybutyrate concentrations of 1.52 mmol/L in plasma (P = 0.036 from baseline; SED: 0.62) and 2.99 mmol/L in urine (P < 0.001 from baseline; SED: 0.36).

Conclusion: In the short term, high-protein, low-carbohydrate ketogenic diets reduce hunger and lower food intake significantly more than do high-protein, medium-carbohydrate nonketogenic diets.

If you are worried about the health effects of such a diet, there was also another new study I saw that had the following conclusion:

Conclusions: A reported higher protein intake appears to confer some weight-loss benefit. Cardiovascular disease risk factors, biomarkers of disease, and serum vitamins and minerals improved with no differences between groups.

These studies back up the argument of Gary Taubes.


Anonymous said...

The second study you cite basically nullifies the first. It shows that in the long term, which is what counts, there is no advantage to the low-carb diet for weight loss or health gains. We all know that month-long diets based on any fad can do amazing things but they never last.

Chris said...

Anon - I don't think the second does nullify the first - they are looking at different things. The first is about hunger, the second is about certain markers of health, one year after the initial 3 month diet. The second doesn't mention hunger.

Additionally the conclusion was that the higher protein intake did confer some weight loss benefits after 564 weeks - i.e. the long term.

Chris said...

obviously he last sentence should read 64 weeks