13 Mar Efficacy of the 6 Major Weight Loss Diets

All weight loss diets can be classified into 6 different types.  Everybody has an opinion about which diet works best.  What does the science say?

1.  Low Calorie Diets – These can be sub-classified into Very Low Calorie Diets (diets providing 400-800 kcal/day) and Low Calorie Diets (those providing 800-1200 kcal/day.)  The Very Low Calorie Diets are usually provided in the form of liquid diets that act as a replacement for all real foods.  They are used to provide rapid weight loss.  Muscle loss on a Very Low Calorie Diet can be a problem with as much as 25% of weight loss coming from muscle.  Resistance exercise can help preserve some of this loss in obese and untrained individuals.  Individuals who have done resistance training consistently in the past will not be able to preserve muscle mass on such a calorie restricted diet.  A Very Low Calorie Diet can be motivating to significantly obese people since weight loss will be more dramatic initially.   Weight loss after one year, however, is no different than those on a Low Calorie Diet.  How long can one stay on a Very Low Calorie Diet safely is debatable.  The standard practice is to stay on a Very Low Calorie Diet no longer than 8-12 weeks before transitioning to a Low Calorie Diet.

2.  Low Fat Diets –  Studies have defined low fat diets quite broadly as diets containing 15-30% fat.  The thought is to limit the most energy dense foods.  Fat contains 9 calories per gram whereas protein and carbohydrates contain 4 calories per gram.  The major determinants of the energy content of food are the fat and water content.  The more fat the food has, the more calories the food will contain.  The more water the food has, the fewer calories the food will contain.  Short term studies (< 1 year) typically reveal better weight loss with a low fat diet than your average low carbohydrate diet, but the difference is only 0.5-1 pound at the end of a year.  Longer term studies show no difference.

3.  Low-Carbohydrate Diets – Low-Carb diets are defined as having < 45% of total calories from carbohydrates.  Some studies define a low carb diet as <200gm of carbohydrates per 24 hours.  Ketogenic diets, which we will discuss next are often defined as having <50 gm of carbohydrates per 24 hours.  Diets whose carbohydrate content exists toward the lower end of the scale tend to perform better that low-fat diets but not typically by more than a pound or two at the end of a year.

4.  Ketogenic Diets –   Ketogenic diets are very low carbohydrate diets.  The theoretical purpose is to not only reduce caloric content but to also change the way insulin breaks down and burns fat.  Because of poor study design, there is disagreement on whether or not weight loss in this type of diet is because of this proposed mechanism or if weight loss is due to the higher protein content associated with this type of diet.  The limited number of studies that actually control the amount of protein in their ketogenic diets do not show an weight loss advantage when compared to standard low carbohydrate diets.

5.  High-Protein Diets – Low calorie, low carbohydrate, high protein diets typically have 30-60% of the total calories from protein or 1.2-1.6 gm/kg body weight.  This is twice the RDA recommendation.  Studies have shown that on this type of diet, lean muscle mass is easier to maintain.  Typically fat loss is also slightly better.  Protein is more satiating than fat and carbohydrates.  Protein also requires more energy expenditure to digest and process.  Fat loss and lean muscle growth are significantly improved when this type of diet is combined with resistance exercise.

6.  Intermittent Fasting – The most well studied type is the alternate-day fast.  In this diet one fasts one day and then alternates with a normal eating day the next day.  In theory people eat fewer calories over a week because one does not completely erase the calorie deficit created on fasting days.  In the most complete review of intermittent fasting versus continuous energy restriction diets, the 2 dieting styles showed similar weight loss and body composition changes.

Take-Home-Message –  All the diet types work similarly with a slight advantage going to the high protein diet.  At the end of a year the difference between all of these diets is approximately a single pound.  A diet only works if you stay on it.  Pick the diet style that you think you can follow the easiest.  Chose the one that is the most palatable for you.  The diet you like the most will be the most effective.

Here’s to the Journey!