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Obesity, Beyond “Calories In, Calories Out”
Sneha Kishore

Obesity, Beyond “Calories In, Calories Out”

What if obesity, or even gaining weight, was not just about the net balance of how much you put in and how much you put out? What if it was a complex relationship of the type of food and its relation to insulin. It has long been said that eating low glycemic index foods are better for you, but why?

An August 2018 article in JAMA (Journal of the American Medical Association), challenges the conventional model of obesity with what is termed as the carbohydrate insulin model of obesity. The conventional model starts with overeating, resulting in increased energy intake and decreased energy output resulting in obesity. The carbohydrate insulin model starts with increased consumption of processed, high glycemic load carbohydrates which produce hormonal changes that promote calorie deposition in adipose (fat) tissue, exacerbate hunger, and lower energy expenditure.

Animal models have clearly shown that dietary composition affects metabolism and body composition independent of calorie intake. Changes in the dietary quality since the 1970’s produce hormonal responses that shift the partitioning of calories toward deposition of fat in tissue, thereby fewer calories remain available in the blood stream for use by the rest of the body, driving hunger and overeating.

Insulin exerts a dominant anabolic control and decreases circulating concentrations of all major metabolic fuels by stimulating glucose uptake into tissues, suppressing release of fatty acids from adipose tissue, inhibiting ketone production in the liver, promoting fat and glycogen deposition. Therefore, increased insulin action like treatment of diabetes is associated with weight gain. Insulin induced weight gain is due to changes in metabolism. On the opposite spectrum, inadequate insulin in Type 1 diabetes and drugs that inhibit insulin secretion cause weight loss.

Dietary carbohydrates have the most potent effect on insulin secretion and participate in the glycemic load. The Glycemic Load = Carbohydrate amount x Glycemic Index. It is the best predictor of post prandial (after a meal) glucose levels.

Protein (depending on amino acid composition) stimulates insulin secretion, but also elicits secretion of glucagon, a catabolic hormone that antagonizes insulin. Dietary fat has little direct effect on insulin.

Low calorie, low fat diets may actually exacerbate the underlying metabolic problem by further restricting energy available in the blood, triggering the starvation response of increased hunger, falling metabolic rate, and elevated stress hormones.

Animal models show that injection of insulin into the central nervous system produces anorexia and weight loss, but injection into the periphery promotes fat deposition, increases hunger, causes weight gain. An interesting note is, even when calories are restricted, insulin treated animals still developed excess body fat. This shows that insulin can be a strong driver of obesity.

Two major trials (Diogenes and DIRECT Trial) found greater weight loss on low vs high Glycemic Load diets.

The carbohydrate insulin model argues that a high glycemic load diet alters the homeostatic mechanisms that prevent weight gain, shifting the baseline weight upwards.

No one dietary factor can fully explain the variations in body weight among individuals and populations. Many hormones (leptin and ghrelin) and the gut microbiome may affect body composition related to, or independently of glycemic load.

The carbohydrate insulin model focuses of high glycemic load carbohydrates because these elicit a greater insulin response calorie for calorie. However, other aspects of a diet ex. protein amount and type, fatty acid profile, micronutrients and nondietary factors ex. sleep, stress, physical activity, environmental and endocrine disrupting chemicals can also affect insulin secretion or adipocyte biology directly.

Emphasis should be on the quality rather than the quantity of calories consumed to shift calorie partitioning away from fat storage and improve metabolic fuel availability to the rest of the body. This could lower the apparent “body weight set point”.

The take home message, based on the carbohydrate insulin model is:

  1. Reduce refined grains, potato products and added sugars
  2. Emphasize low glycemic index carbohydrates, non-starchy vegetables, legumes, non-tropical fruits.
  3. Choose whole kernel grains like whole barley, quinoa, stone ground flour.
  4. Increase nuts, seeds, avocado for healthy plant-based fats
  5. Maintain adequate but not high intake of protein from plant sources (these are less insulin stimulating that animal sources).
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