low glycemic index editorial

i will editorialize on a recent editorial in JAMA, which argues that adiposity may be the cause and not the consequence of overeating (see obesity as cause for overeating jama2014 in dropbox, or JAMA. 2014; 311(21): 2167). this editorial was written by david ludwig at boston childrens hosp, founder of the OWL clinic there (optimum weight for life), and longstanding champion of low-glycemic index diets (he wrote the seminal article on it -- at least from what i've seen -- in 2002, which reviews data and provides a theoretical framework --see glycemic index ludwig jama 2002.pdf in dropbox, or JAMA. 2002; 287(18): 2414). isuspect that the effectiveness data on low GI diets for weight loss, which is really no different from other diets, has more to do with the ability of patients to adhere to the diet long-term, as opposed to the specific diet itself. hard to adhere longterm when people are bombarded with calorie-dense, high carb foods (advertising, low-cost, high presence and availability in many areas including inner city and rural areas).  the gist of his argument is as follows:

    --effectiveness of weight loss programs is okay short-term, but maintenance at 1 year is pretty miserable

    --feeding studies show that changes in energy balance lead to compensatory mechanisms that antagonize the energy balance change (eg study of 41 people underfed or overfed to achieve 10-20% weight change led to compensatory change in energy expenditure -- ie, underfed people tend to decrease energy expenditure as compensation to decreased energy intake and vice versa)

    --the body has a pretty tightly controlled blood supply of energy (combo of major metabolic foods of glucose, nonesterified fatty acids, ketones), and any acute decrease or oxidation of them leads to intense hunger/food intake (an increase through fatty acid synthase inhibition or b3-agonist intake lowers food intake). 

    --insulin, an anabolic hormone, is important regulator of body weight: it drives glucose and non-esterified fatty acids into storage and is associated with weight gain. decreased insulin levels assoc with wt loss. fatty acid synthase expression is increased in fat tissue by insulin.

    --low-glycemic index diets decrease insulin levels (and, studies in rats given iso-caloric high vs low glycemic index diets develop hyperinsulinemia, and disproportionately more fat accumulation, even if put on food-restricted diet to prevent weight gain).

    --there are also other factors which decrease anabolic drive, such as low refined-sugar intake, high polyunsat vs sat fats, low trans fats, high omega-3 intake, probiotics, etc; and physical activity, sleep and stress can affect calorie uptake and storage

    --a small study by ludwig found that overweight or obese young adults achieving 10-15% weight loss with a variety of iso-caloric diets found that those on the low-fat (60% carbs) and low glycemic index (40%carbs) diets had decreases in both the resting and total energy expenditures as compared with the very low carb diet (10% carbs), and this decrease in energy expenditure tracked with the % of carbs in the diet.  ie, there seems to be a compensatory mechanism for weight loss by decreasing the energy expenditure, which is significantly less of a decrease with lower carb ingestion (see low GI diet and energy expenditurejama 2012 in the dropbox, or JAMA. 2012;307(24):2627-2634.

so, would be great to have real data showing the long-term effectiveness of low glycemic diet interventions. however, i find his arguments pretty compelling and have suggested low-glycemic index diets for many years now, to help with weight loss (mildly successful), diabetes control (pretty successful), and lipid improvement (pretty successful in decreasing triglycerides, increasing HDL, and improving cholesterol:HDL ratios). would be great if we could have public health programs which really promote healthy eating, increasing the accessibility/cost of healthy foods while decreasing those of calorie-dense junk and high carb foods....