Metabolic Changes in Low Carbohydrate Diets

Low-carb diets are in vogue, thanks to their effectiveness at helping dieters trim fat quickly, but they have pros and cons. Two drawbacks are the restrictive food choices and the psychological difficulty in sticking to the diet in social settings. However, you might not know that long-term low-carb dieting can have an adverse effect on metabolism. If you or someone you know is thinking of using a low-carb diet for a long period of time, read on before making a final decision.

Low-Carb Diets and Insulin

• Insulin is a storage hormone that the body produces to shuttle nutrients into both fat and muscle tissue. Normally produced in response to elevated blood glucose levels after carbohydrate consumption, insulin levels on a low-carb diet remain fairly low. While this is initially a good thing, as regulation of insulin levels can have a positive effect on body composition, decreased insulin levels over an extended period of time can have a negative effect on levels of leptin, a metabolic hormone.

About Leptin

• Leptin is a hormone that "talks" to the body's hypothalamus. Its primary job is to tell the body whether it has the go-ahead to use adipose (fat) tissue for fuel. Where leptin is plentiful, this process is carried out without any problems. However, where insulin levels are low over a prolonged period of time, leptin levels are correspondingly low, which can negatively impact the metabolism, making it run slower.

Leptin and Metabolism

• Low leptin levels mean that the brain is not receiving signals regarding utilizing fat as an energy source. The brain responds to this by assuming something is wrong, and switches into panic mode, sending out signals to the rest of the body to decrease thyroid output and metabolism, and to increase production of cortisol, a hormone that leads to fat gain if elevated for too long.

Positive Effects of Low-Carb Diets on Metabolism

• Of course, the effects are not all negative. Consuming a low-carb diet means that your protein intake will rise by virtue of macronutrient replacement -- as you will not be eating carbs, you will have to replace those calories with something. Increased protein intake can positively affect metabolism by utilizing the thermic effect of food. The thermic effect of food merely states that it takes calories to digest food, with protein requiring the highest "cost" of digestion. Therefore, you will be burning extra calories simply by virtue of consuming additional protein in your low-carb diet. Increased protein intake affects the metabolism, which in turn affects body composition. Thus, you will lose weight faster on 1,500 calories of protein than you would on 1,500 calories of any other macronutrient, as the body is expending more calories just to digest the protein.

Considerations

• Remember that while extreme low-carb dieting can have a negative effect on metabolic processes over the long-term, that does not mean you must eschew low-carb as a short term option for fat loss. Another viable alternative is to have a bi-weekly "carb-up" -- a day where you consume a few hundred grams of carbs to restore leptin function while on a low-carb diet. Using either carb-ups or sticking to low-carb dieting just for a short time can avoid these negatives while still providing all of the benefits of a low-carb diet for fat loss.