What is the best diet to lose weight?

What is the best diet to lose weight?

What is the best diet to lose weight? This is a question to which we can find all sorts of answers. Some will be motivated by the sale of products ( books, nutritional products, life coaching, etc. ) and, strangely, very few will have a real objective trend. We quickly fall into opinion and anecdotal without forgetting those who will tell science what it does not say.

Aragon et al., Looked at the issue and following a literature review came to conclusions leading to an official position taken by the International Society of Sports Nutrition. Authors and collaborators have peeled the scientific literature to highlight which diet is most effective for weight loss. Some frown when it comes to scientific studies, fearing bad lobbies and corrupt researchers. However, I still prefer to take notice and understand what scientific studies are doing before blindly believing what is possible to read and view on the Internet (because of course, there is no lobby and financial interest on social networks, people only want to educate you and enlighten their lantern, because they are similarly fine ).



The authors subdivided the universe of diets for weight loss into 7 archetypes:


  • Low-calorie diets
  • Severe hypocaloric diets
  • Low-fat diets
  • Low carb diets
  • Ketogenic diets
  • High protein diets
  • Intermittent Fasting

The studies reviewed should be longer than 4 weeks, with or without exercise, and have valid body composition measurements.

Before answering the question, here is a brief description of each of the observed archetypes.

Low-calorie diets and severe low-calorie diets

Low-calorie diets provide between 800 and 1800  kcal per day in energy intake. The goals of these diets are to stimulate rapid weight loss, usually in the range of 1.0 to 2.5  kg per week while preserving muscle mass. Severe hypocaloric diets provide between 400 and 800  kcal per day in energy intake, usually in the form of meal replacements ( solid and liquid forms ). Generally, the macronutrient content of this type of diet is 70-100  g protein, 15  g fat and 30-80  g carbohydrate daily.

Low-fat diets

These diets are defined by their contribution to lipids ( 20-35 % of the total energy contributions in the form of lipids, sometimes even up to 10  % only ). The breakdown in macronutrients usually follows the following profile: 10-35 % protein, 45-65 % carbohydrates, 20-35 % lipids.

Low carb diets

Diets that provide less than 40-45 % of total energy intake in the form of carbohydrates are included in this category. Usually, one consumes less than 200  g of carbohydrates per day, but more than 50  g.

Take responsibility for losing weight and hypertrophy
Ketogenic diets
These diets rely on an increase in the circulation of ketones through a minimal consumption of carbohydrates ( ~ 50  g per day or ~ 10  % of total energy intake in the form of carbohydrates ). Protein intake is around 1.2 to 1.5  g of protein per kg of weight per day and most of the energy ingested is in the form of lipids ( ~ 60-80 % of the total energy intake in the form of lipids ). One of the main arguments behind the significant reduction in carbohydrate consumption is based on increased lipid oxidation following a decrease in insulin levels.

High protein diets

A diet is considered high protein when daily protein intakes exceed 25  % of total energy intake or more than 1.2-1.6 g of protein per kg of body weight per day. These diets are based on 2 main elements; 1) the effect of protein on satiety ( decreased appetite ), increased food thermogenesis ( protein digestion costs about 30  % of calories in protein, compared to ~ 6-8 % for carbohydrates and ~ 2-3 % for lipids ).

Intermittent Fasting
There are different ways to perform intermittent fasting: 1) alternating day ( fasting day, normal feeding day ), 2) sporadic fasting ( 1 or 2 periods of 24  hours of fasting per week ) and 3) fasting chronic ( daily fasting from 16 to 20  h with a recharge period of 4 to 8  h ).

Now, what about the scientific literature about diets and weight loss? I summarize the main lines …

Regardless of the diet, fat loss is caused by an energy deficit for a long enough time. This caloric restriction can be linear ( restriction every day ) or non-linear (calorie restriction over a day total, for example, the energy deficit is obtained over 1 week, but not necessarily every day). The higher the initial fat, the higher the initial caloric restriction can be. 
Once weight loss has begun, it is possible to gradually slow down weight loss to maintain lean body mass ( ~ 0.7  % weight loss per week ).
Weight loss diets based on decreased fat or decreased carbohydrate seem to have similar results. The authors mention that, to date, no study comparing diets using isocaloric protocols and where protein intake is similar in all groups, has shown a higher fat loss or thermogenic effect for one or the other approaches.
An increase in protein intake together with an energy deficit seems to favor the loss of fat mass. Inputs as high as 1.4 to 2.0  g protein per kg bodyweight daily could be an effective strategy for weight loss.

Overall, intermittent fasting strategies do not seem more effective than more traditional caloric restriction ( linear or non-linear ).

Am I right to exist professionally?
So for the moment, no matter what the diet is, the results will not necessarily be better or worse if you exclude the increase in protein intake. A lot of carbohydrates, not a lot of carbohydrates, a lot of fat, not a lot of fat, same results in weight loss.

However, other elements are to be considered in order to make a round-up a little more complete …

The principle of energy balance still holds, the relationship between calories consumed and calories burned/used dictate changes or lack of change in body composition. However, macronutrients do not all have the same impact on the energy balance. If in the end, it is a simple mathematical operation, the path to calorie values “in” and calories “out” is excessively sinuous and complex.

At first, the effect of macronutrients is not the same on the energy cost of digestion ( you remember, it costs 30% to digest protein, 6-8 % for carbohydrates and 2-3 % for lipids ). However, this impact is relatively small over a 24-  hour period. Usually, the energy cost associated with the digestion and assimilation of nutrients is of the order of 8 to 15 % of total energy expenditure. The variations of this compartment of the total energy expenditure are thus rather weak and have little impact on a deficit or a surplus energy and thus of the body composition. Small note, processed foods tend to be more easily assimilated by the body, which slightly reduces the cost of digestion. Wright et al. Found that consumption of processed ham sandwich versus homemade ham sandwich with “unrefined” products resulted in lower food thermogenesis ( 73  kcal vs. 137  kcal).). But before jumping to the conclusion that processed products are more fattening than less processed products, it should be remembered that many successful weight loss interventions have used highly processed products such as meal replacements ( which brings us back to the energy balance and the importance of the calorie deficit ).

Then, the most energy-consuming compartment in the majority of the population is the resting metabolism ( ~ 60-70 % of the calories spent on a day for an average person ). Once again, nutritional intake influences this compartment slightly. The resting metabolism ( less than kcal per min ) is slowed down by about 10-15 % during a complete fast that lasts more than 48  hours. A partial calorie restriction will, therefore, have a lesser effect on the resting metabolism. Weight loss leads to a decrease in resting metabolism ( less than total kcal per day ) at approximately 13-16  hours.kcal per kg of muscle and 4.5  kcal per kg of fat. These values remain negligible and have, in the vast majority of cases, little impact on the energy balance.

Why are you wasting your time with a nutritionist …

We still have one last compartment, that of energy expenditure associated with physical activity. This compartment includes all physical activities, not just training. It is probably here that diets may have the greatest impact. There is a decrease in total energy expenditure ( Rest metabolism + food thermogenesis + physical activity ) in individuals losing more than 10  % of their total weight. Weight loss leads to a decline in normal resting metabolism ( less fat and possibly less muscle, so less energy spent at rest) which inevitably has an impact on the total calories spent on a day. However, as mentioned earlier, this impact is relatively negligible. Nearly 90  % of the decrease in total energy expenditure is associated with a decrease in energy expenditure associated with physical activity. The main “energy” risk of a diet is to make people spend less energy either by moving less or by moving with less intensity.

This is a critical point, as simple replenishment ( cessation of diet, increased energy intake ) does not systematically lead to an increase in energy expenditure associated with physical activity. We are thus in a situation where in addition to gaining weight, the person is likely to suffer a decrease in his physical condition.

In conclusion, what is the best diet to lose weight?

It seems interesting to increase protein intake when trying to lose weight by creating an energy deficit, but besides protein, the composition of the diet seems to have little effect on the extent of weight loss… Also, it is critical to consider the impact of energy expenditure associated with physical activity on all calories burned daily as well as the impact of a diet on this compartment. The diet chosen to lose weight should help maintain or even increase the energy expenditure associated with physical activity to minimize the risk of weight gain after surgery.


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