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Skinny Without Willpower

Sunday, March 15, 2009


How many times have you heard “The fat in pizza will make you fat” or “the fat from deep fried foods will make you fat”? Countless, right? But truth couldn’t be farther than this. I myself believed, for the longest time, that a high-carb low fat diet is the holy grail of weight loss. But little did I know...

The recent interest in Atkins and South Beach diet and all the related success stories have compelled researchers to re-think the “fat will make you fat” mentality. To understand this, one has to understand the mechanism by which fat is stored in the body and the role of Insulin in weight gain. Fat in the diet converts to fatty acids and carbs in the diet convert to glucose in the blood stream. The role of pancreas in the body is to regulate blood glucose levels and when ever the glucose level in the blood rises, the pancreas produce insulin to counteract it. The insulin then takes away the blood glucose and converts it into glycogen that is stored in the liver and the muscle cells. Once the muscle cells and liver reach their full glycogen storage capacity any excess glycogen converts to fat. This is where added muscle mass from weight training comes in handy for storing the glycogen and prevent fat conversion. Fat doesn’t get stored as fat until it is acted upon by insulin and figure 1 shows how the blood glucose level rises with time after ingesting a carb or fat meal. It’s clear that fat doesn’t cause a rise in blood glucose level and neither does it elicit an insulin response from the pancreas as illustrated in figure 2.

Figure 1. Blood glucose levels after 100g of carbs or 40g of fat. [Ref 1]

Figure 2. Blood insulin levels after ingesting 100g of carbs or 40g of fat. [Ref 1]

The other aspect of this scenario is the delayed response of the glucose/insulin system. From figure 1 you can see that the blood glucose levels come back to normal levels within about 90 or so minutes while the insulin levels remain high, this causes your blood glucose to fall below normal levels, making you hungry again. As a result you consume more carbs. This sets off a vicious cycle, which if continued for long periods of time, makes the body insulin resistant and the more you eat the more insulin gets triggered causing more weight gain and more hunger pangs, making obesity inevitable. [Ref 2, 3]. The other affect of insulin is to suppress the production of Lipase, a hormone responsible for metabolizing fat in the cells into fatty acids.

The only way fat from diet gets stored as fat in the body is when insulin acts upon fatty acids and drives it into cells as stored fat. And from figure 1 and 2 its easy to see why fat by itself cannot contribute to weight gain. But if fat is consumed with carbs then it would contribute to fat gain. No wonder pizza, donuts and cheeseburgers are some of the most notorious weight gain foods because they combine fat with carbs.

So now that you have gained weight the next question is how to lose it? Well, the only way to lose fat is to metabolize it into fatty acids and use up as energy. This will happen in one and only one condition, that is, when you deprive the body of its present source of energy, glycogen. This can only happen by:

1) Starving.
2) Limiting the consumption of carbs and relying on fat and protein as the primary source of energy.

Obviously the first approach doesn’t work as it slows the metabolism and forces the body to go into starvation mode, thus making further fat loss impossible. The second approach is the gist of all the modern weight loss diets. The Atkins relies on protein and fat as the primary source of energy with very little carb. The South-Beach relies on high protein, ‘healthy’ fats and limited quantities of ‘healthy’ carbs for fuel. But what is a ‘healthy’ carb? This begs the question: are all carbs created equal? This is a topic for my next post…


1. Robertson MD, Henderson RA, Vist GE, Rumsey RDE. Extended effects of evening meal carbohydrate-to-fat ratio on fasting and postprandial substrate metabolism. Am J Clin Nutr 2002; 75: 505-510.

2. Bruning JC, Gautam D, Burks DJ, et al. Role of brain insulin receptor in control of body weight and reproduction. Science 2000; 289: 2122-5.

3. Odeleye OE, de Courten M, Pettitt DJ, Ravussin E. Fasting hyperinsulinemia is a predictor of increased body weight gain and obesity in Pima Indian children. Diabetes 1997; 46: 1341-5.

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