Which diet is best for weight loss?

There are so many diets and conflicting information promoted in the media. This creates a maze of messages making it impossible for the general public to navigate to the truth of what type of diet is best for improving body composition and in particular fat loss.

What we need is a trusted body to go over all the valid scientific research to date and just tell us what diet works and what’s just bullshit getting sold to us. Well that has happened. The Journal of International Society of Sports Nutrition went over all the research intervention trials up to the date of publishing in May 2017.

This is a snapshot of what I took away from the examined research of the various types of diets and the findings that were published in the full article here https://jissn.biomedcentral.com/articles/10.1186/s12970-017-0174-y.

DIET TYPES

 

There is a vast multitude of types of diets. It’s difficult to sort out what is actual evidence and what are simply claims. I’ve tried to simplify the results of the study as best I could. The study started with the following different types of diets:

Low-Energy Diets (800-1200 Calorie Diets) and Very Low Energy Diets (400-800 Calorie Diets)

Very Low Energy Diets are usually diets that are made up of liquid meal replacements that are designed for rapid weight loss. Research suggests that 25% of the total weight loss in these extreme diets can be attributed to lean muscle. Resting metabolic rates therefore significantly decreased in this group. However, if you are untrained and Obese, lean muscle can be preserved along with your resting metabolic rate by including an appropriate resistance training program. Very low energy diets could be of benefit in obese populations because a greater initial weight loss is sometimes associated with a greater chance of long term success. However, when comparing very low and low energy diets there is research that reports no difference in long term weight loss and the lower the calorie intake, the more chance there is of adverse effects like fatigue, headaches and dizziness. The higher the baseline fat level, the more aggressively the caloric deficit may be imposed. As subjects get leaner, slower rates of weight loss can better preserve lean muscle.

Low Fat Diets (20-35% of diet made up of fats)

By following a low fat diet, total energy intake can be reduced, therefore reducing body fat over time. The premise of a low fat diet is to reduce the macronutrient that is the most calorie dense and therefore reduce total daily calories. Body composition improvements is not necessarily from the reduced fat intake but from the reduced calorie intake.

Very low Fat Diets (10-20% of diet made up of fats)

Vegetarian and Vegan diets fit this description. There is consistent evidence to support very low fat diets positively promoting weight loss. However, there is no difference when compared to other diets of higher fat intakes when calories are the same and this is a big one, adherence to such a low fat intake can be difficult for people.

Low Carb Diets (<45% of diet made up of carbs)

There is some evidence to support low carb diets positively effecting body composition. Low carb diets tend to default to a higher protein intake which could explain the benefit of low carb diets on body composition.

Ketogenic Diets (<10% of diet made up of carbs)

There is evidence to suggest the Ketogenic diet promotes weight loss. Its proposed that the extremely low carbs enhances fat oxidation. When protein and calories are the same between two groups, it makes no difference to fat loss or does it provide a thermic advantage if the remaining calories is made up of carbs or fat studies show.The evidence therefor invalidates the carbohydrate-insulin hypothesis of obesity. However, ketogenic diets have shown appetite-suppressing potential The high protein intake on a ketogenic diet is the crucial factor in promoting weight loss. Even slightly higher intake of protein when on a Ketogenic diet can dramatically improve fat loss. Protein is such a satiating macronutrient and the likely reason of the fat loss benefits of a Ketogenic Diet. Sticking to extremely low carbs is also challenging to adhere to long term for a lot of people.

High Protein Diets (1.2 -1.6g/kg of body weight)

High Protein Diets have a substantial evidence basis for improving body composition, particularly when paired with training. Of the macronutrients, protein has the highest thermic effect (burns the most calories when your body metabolises it). The total Thermic effect of food accounts for 8-15% of total daily energy expenditure. Higher protein intakes preserve resting energy expenditure while dieting. Resting Metabolic Rate, the energy expenditure at rest can be as much as 10% more due to the residual influence of the Thermic Effect of food and physical activity.

While dieting following a hypocaloric diet, a high protein diet combined with resistance training can prevent loss of lean muscle. Also, protein is the most satiating macronutrient. There is no evidence to suggest a very high protein diet (3-4 times RDA) has any adverse health effects. In fact, there is growing evidence that super high protein diets have a positive impact on body composition in trained subjects.

Intermitted Fasting

There is strong evidence that intermitted fasting out performs daily calorie restriction for improving body composition. A positive for intermitted fasting is that it doesn’t require calorie counting. Fat loss occurs with alternate day fasting because there is an overall reduced calorie intake. Lean muscle mass loss occurs however. There is evidence that points to having one meal a day at lunchtime instead of fasting the whole day is better at preserving muscle. When comparing fasting to just a normal calorie restricted diet (eg. The same calories over the whole week/month) there is no benefit to fasting over daily calorie restriction in terms of fat loss. It may be easier to stick to however most likely because intermitted fasting allows for freedom of food choice on non-fasting days and also no calorie counting is involved.

Summary

A wide range of dietary approaches (low-fat to low-carbohydrate/ketogenic) for the most part, can be similarly effective for improving body composition. Personal preference can therefore be used when selecting a diet, as long as a few principles are adhered to:

  1. Operate under the fundamental mechanism of a sustained caloric deficit to reduce body fat. This net hypocaloric balance can either be imposed linearly/daily, or non-linearly over the course of the week. Therefore, linear versus nonlinear caloric deficits should be determined by individual preference and tolerance.
  2. Adequate – high protein intake is required to maximize muscle retention while in hypocaloric conditions.
  3. Resistance training, and an appropriate rate of weight loss (unless obese) should be the primary focus for achieving the objective of lean muscle retention during a hypocaloric fat loss diet.

Luke Wardle is an Exercise Scientist and Director of Legion Fitness Living.

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