Insulin and Carbs

Why Exercise Alone is Not the Answer
Let’s start right off dispelling one of the most common myths about the positive effects of exercise on weight loss. The truth is exercise is a rather lousy weight loss tool, but it is a great wellness tool. The strongest evidence showing weak effects of exercise comes from studies done in identical twins under highly controlled conditions where all food was provided and exercise carefully monitored. In one experiment twins were fed a caloric level to maintain body weight. Then on top of that they were required to exercise for 2 hours per day for 3 months. This created a daily energy deficit of over 600 kcal for each person in the study. That equals an energy deficit of more than 58,000 kcal total. If it takes a deficit of 3500 kcal to lose one pound of fat, these subjects should have lost more than 16 pounds. The most striking finding was the wide discrepancy in weight loss among the twins ranging from 2 to 18 pounds. Think about how disappointing it would be to lose only 2 pounds after diligently exercising for 2 hours per day. Even more striking was the discovery that the weight loss within twin pairs was very similar. Since identical twins share the same DNA, this study clearly shows that your genetics plays a huge role in your weight loss response to exercise. 

If Exercise is Not the Answer for Everyone, What Is?
The previous example is not meant to downplay the importance of exercise, since exercise does promote many positive health effects and resistance training is necessary to build muscle. But it does highlight the fact that exercise has weak effects in promoting weight loss and underscores the importance of paying attention to diet composition. Many experts will say all you need to do is eat less than you expend to lose body weight. This is exactly the wrong way to look at the situation. If you are trying to lose weight, what you really need to do is lose body fat. Although you may view that fat as unhealthy and unsightly, it actually represents your body’s largest fuel tank. And that fuel can be used in a positive way. Wouldn’t it be a neat trick to mobilize that fat and convert it into a reliable and consistent form of energy your body used all day long? That’s currently not the case since access to that fuel tank is being blocked by eating the wrong foods. The trick to unlock the flow of fat from your fat stores is to keep the hormone insulin in check. 

Keeping Insulin Low
Insulin has many functions in the body, most notably increasing blood sugar uptake into cells, but here are three additional functions of insulin that emphasize why you will benefit from keeping this storage hormone low. 

First, of all the various mediators that regulate fat breakdown, insulin is the most important. Fat, or more specifically fatty acids, are primarily stored as triglycerides in fat cells (i.e., adipocytes). A triglyceride is simply three fatty acids attached to a single glycerol molecule. In order to access those fatty acids you have to release them from glycerol. This process of fat breakdown is called lipolysis. Insulin potently blocks lipolysis. In other words insulin prevents fatty acids from being released from fat cells. The relationship between insulin and fat breakdown is not linear. Small increases in insulin cause a major inhibition of fat breakdown. 

Thus, when you raise insulin levels by consuming fast acting forms of carbs, it puts the breaks on fat breakdown both at rest and after exercise. 

A second factor relates to oxidation (i.e., burning) of fat which occurs mainly in muscles. More specifically, fat oxidation occurs in specialized energy-producing structures called mitochondria. Once a fatty acid enters the mitochondria it is committed to being burned and therefore this is the rate limiting step in burning fat. Fatty acids can only enter mitochondria by a specific transporter. Like fat breakdown, this mitochondria transporter is under tight control by insulin. Insulin potently inhibits this fatty acid transporter and thereby blocks fat burning. Thus, when you spike insulin levels, it inhibits both fat breakdown and fat burning. 

Third, insulin’s effects are not limited to suppressing fat breakdown and oxidation; it also promotes storage of fat. The insulin response to a high carbohydrate meal functionally blocks access to fat for fuel and at the same time promotes conversion of carbohydrate into either glycogen or fat. Insulin does this by increasing the activity of key enzymes that control synthesis of fat in the liver and uptake of fat into fat cells. Therefore, over time repeatedly spiking insulin contributes to accumulation of body fat. 

Bottom line, keeping insulin low is the key to shifting your body’s metabolism toward burring fat as the body’s primary fuel. Finding the level of dietary restriction of sugars and fast acting starches required to enable the preferential burning of body fat is the essence of a successful weight loss program. 

Diet from an Evolutionary Perspective
If restricting carbohydrates seems unbalanced or even extreme, consider the fact that as humans we are well suited to respond in a positive way to carbohydrate restriction as in high energy levels, better satiety, and enhanced ability to lose body fat and maintain health. This stems from more than 2 million years of evolution when most of us were exposed to very little carbohydrate. Therefore, this favorable response to low carbohydrate intake is a highly conversed trait. Now that most of us are exposed to a lot of carbs, many of us struggle to maintain a healthy weight and show signs of metabolic dysfunction. The ability to respond favorably to increasing amounts of carbohydrate is a trait that fewer and fewer people possess (i.e., it’s a less conserved trait). In other words, if you try a low fat/high-carbohydrate diet, there is a good chance you may not respond in a positive way, no matter how much drive and determination you put into it. This is not your fault. It’s not a problem with you; rather it’s the wrong diet for your body’s metabolism. Chances are if you have failed on a high carbohydrate diet, the right diet for you is one lower in carbohydrate.

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