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Weight regulation 4: Low carbohydrate vs. low fat lifestyles for weight loss and maintenance

After my digression into the 2010 Dietary Guidelines I am resuming my series on weight regulation with a comparison of the two major methods of achieving weight loss. I was tempted to call these weight loss diets but to regulate weight in the long term it is necessary to make a lifestyle change.  One can’t go on a diet and then go back to eating the way she always did and expect to maintain the weight loss.  Let me state at the outset that both of these methods work for taking off weight.  However, there is great metabolic variability among people; one size does not fit all.

Most people are familiar with low calorie diets.  These are the ones recommended by the majority of physicians, dietitians and weight loss programs like Weight Watchers.  They subscribe to the idea that calories taken in must be less than calories expended.  Generally, women are limited to about 1200 calories a day and men to about 1500, and it is recommended that a weight loss of 1 to 2 pounds a week is optimal.  In order to keep the calories down to those levels it is necessary to strictly limit fat consumption because of its higher caloric density.  Therefore, low fat diets are by necessity high carbohydrate diets, since protein intake should optimally be kept around 15-20% of calories. High carbohydrate diets must be calorie restricted because of our ability to easily over-consume carbohydrates. Sticking to the diet requires strict monitoring of intake, sometimes even weighing and measuring of all food.  These eating regimens result in weight loss for many people but some find that they do not lose when following this plan, probably due to the excessive insulin produced in order to clear large amounts of glucose from the blood.  Since calories are curtailed the body often goes into panic mode, thinks that it is starving, and begins to conserve energy.  The whole metabolism can slow down and with it weight loss. Calorie restriction leads to calorie conservation by the body, making it much harder to lose or maintain weight. Once the weight is lost it is necessary to follow a restricted calorie plan in order to maintain the weight loss.

Low carbohydrate diets are much less familiar to us and have been, until recently, perceived as dangerous, faddish, and unsuccessful in the long term by medical and nutrition experts.  Basically, the low carbohydrate diet must be higher in fat to make up for the uneaten carbohydrates.  It may be slightly higher in protein but is not a high protein diet.  Excess protein, beyond what the body needs for growth and repair of tissues, will be converted to glucose and used for energy, a waste of an expensive nutrient.  The idea behind this diet is that the body learns to use fat for its energy needs rather than glucose, thereby driving body fat out of storage.  Ingested fats are also used for energy needs as well as structures.  Carbohydrate restriction, not negative energy balance, is responsible for initiating the metabolic response to fasting.  In one study (Klein & Wolfe, 1992) infused lipids did not alter the breakdown of fat stores in fasting individuals.  In other words, in the absence of carbohydrate, ingested fat is not stored and doesn’t prevent the body’s use of stored fat.  Low carbohydrate diets are much less likely to initiate a starvation response by the body.  Therefore, once the weight is lost the dieter can add back just enough carbohydrates to maintain weight but otherwise does not need to restrict calories.

Many think of the low carbohydrate diet as being initiated by Dr. Atkins in the 1970s but forms of this dietary approach have been around for about 150 years.  Until about 10 years ago, however, no one had done any experimental studies of low carbohydrate diets to find out what the real effects are, even though there were thousands of anecdotal accounts of weight loss without hunger and without calorie restriction on these diets.  The first scientific study (Foster et al. 2003) compared the low carbohydrate diet recommended by Atkins with a standard low-fat low- calorie diet in two groups of overweight subjects.  Their results showed that the people on the low carbohydrate diet actually consumed more calories per day, lost more weight over 6 months, and also had higher HDL cholesterol and lower triglyceride levels than the subjects on the low calorie diet. This study has been followed by several more (e.g. Volek et al. 2004, Gardner et al. 2007, Shai et al, 2008) that essentially have shown the same thing—more weight loss and better lipid profiles on a low carbohydrate diet.  It wasn’t the dietary fat that mattered, it was the carbohydrate.

To sum up, low carbohydrate diets are not usually calorie restricted because they are naturally self-limiting.  Low-fat low-calorie diets must be calorie restricted because of our ability to over-consume carbohydrates, and because of what carbohydrates do to our insulin levels.  Both of these regimens work for weight loss, as least in some people.  In general, many health-related biomarkers improve with weight loss on either regimen, but consistently studies find higher HDL levels and lower triglyceride levels in subjects on low carbohydrate diets. Both can be nutrient dense if the correct whole unprocessed foods are chosen.  Low carbohydrate does not meant no carbohydrate.  It is most efficacious when lots of vegetables and some fruits are eaten, but starchy vegetables and flour products are avoided.  The fats eaten on both diets should be the natural variety—butter, olive oil, coconut oil, lard, and not the highly processed vegetable oils and margarines.  Low-calorie diets must make every calorie count by using whole, nutrient-dense foods and eliminating highly processed sugar and starch-laden options.  Finally, either we reduce carbohydrates and eat more natural fats, or we eat more carbohydrate and cut back on fat. To work long term either regimen must be followed for life.  High carbohydrate cannot be combined with high fat—that’s a recipe for weight gain. As far as long-term health and ease of weight maintenance goes it looks like low carbohydrate higher fat is the winner here, but like I said, everybody is different.

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