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A Review: Common Diets

Nutrition is an extremely complex subject and the goal of this review is not to not determine the “best” diet, but rather pull upon the current data of various diet types and draw common themes that, no matter what your eating habits are, you can apply.


One thing to be clear going forward, there is no perfect diet. In fact, one should first consider their lifestyle and pick dietary solutions to best match their individual needs and circumstances. This is for two reasons.


A woman uses chopsticks to serve you food from a bowl.

Firstly, to a large extent, nutrition is behaviour based. Despite this, many people first start by thinking about which diet is “best” and build their plan around that. Even though there are some key themes that will be touched on in this review that may benefit you, the main idea should be to reverse engineer instead the process by asking this question first: What are my current eating habits and lifestyle and what diet strategy can best match that?


Secondly, as you will see in the various diets, except for a few exceptions, all diet structures are effective in producing weight loss. Once this is established, you can best match the diet structure that best fits your needs.


In this review, we will be talking about the following diet types and their relevant changes and maintenance to body composition:


Low-fat diets


Definition

A low-fat diet is defined as having 20-35% of the diet consisting of fats.


Mixed vegetables in silver chafing dishes.

Consideration

This diet structure has the support of major health organizations due to the large evidence base, flexible macronutrients (macros) and does not limit certain foods (1). Fat is the most dense macronutrient providing the most amount of energy per gram of fat at 9 calories per gram. For reference, protein and carbohydrates have less than half that content, both being 4 calories per gram. Therefore, the logic behind the low-fat diet is twofold:

  1. limiting the densest macronutrient will reduce the likelihood of overconsuming calories, and

  2. because fat is limited, both carbohydrates and protein need to be increased.

A common theme in this review is that increased levels of protein, rather than the “diet” itself, is a primary driver of weight loss success.


To see the effectiveness of low-fat diets, a recent review analyzed 32 studies amounting to 54,000 subjects with a minimum duration of 6 months that reduced fat content but kept the other macronutrients similar and demonstrated a modest but consistent reduction in body weight, body fat and waist circumference (1). This demonstrates that simply decreasing fat content has a positive effect on weight loss due to less total energy intake being consumed.


​Key Point

A common theme in this review is that increased levels of protein, rather than the “diet” itself, is a primary driver of weight loss success.


Low carbohydrate diets


A plate of pasta with meat sauce.

Definition

Diets with under 45% of total carbohydrates technically are classified as a low carbohydrate diets. This is because the acceptable macronutrient distribution range (AMDR) is between 45-65%. However, a better definition of having no more than 40% of the diet coming from carbohydrates is classified as low carb.


Consideration

Success is largely attributed to the higher protein intake as well as flexibility in food choices as this form of diet does not prohibit foods based on fat content (1).