Metabolic Typing Diet: Does It Really Work?

The metabolic typing diet is based on one's ability to use macronutrients. But does it work? We'll tell you the answer here.

Reviewed and approved by the nutritionist Maria Patricia Pinero Corredor.

Written by Maria Patricia Pinero Corredor

Last update: 27 May, 2023

Each person inherits a type of metabolism according to their genetics. This explains why some diets work well for some, but not for others. The metabolic typing diet is based on a higher or lower intake of certain nutrients, according to the body’s metabolic response.

This dietary model was developed by metabolic research specialists William Walcott and Trish Fahey. It was introduced in 2001 as a method aimed at weight loss. Since then, it has had a few variations and has gained a worldwide following. But does it work? Here we tell you about it.

What is metabolism?

To begin with, it is worth remembering that metabolism is the “road map” of the thousands of chemical reactions that occur in the body’s cells. It’s driven by enzymes, which are what use the macronutrients (proteins, carbohydrates, and fats) to keep the cells alive and thus carry out their functions. Vitamins and minerals collaborate with these enzymes.

Metabolic pathways produce and release energy by breaking down very complex molecules such as starch. In turn, other pathways use that energy to build compounds necessary for body function. However, if too much energy is produced and not used, fat accumulation and weight gain occur.

What is the metabolic typing diet?

The metabolic typing diet is based on individual differences in the degradation of macronutrients once they are absorbed. According to this, a personalized diet plan is made that takes into account the type of metabolism of each individual. For example, it could be a high-carbohydrate diet or a low-fat diet.

The faster a person’s metabolism, the less time it takes to convert nutrients into energy. But if the person’s metabolism is slow, then it stores nutrients as fat instead of using it. According to Walcott and Fahey’s book, variations in metabolism are due to two hereditary factors:

1. The functioning of the autonomic nervous system

The autonomic nervous system of the body is divided into the sympathetic and parasympathetic systems. These oppose each other in a variety of bodily functions. For example, the sympathetic helps the body respond to stress, while stimulating adrenaline production and energy burning.

The parasympathetic, on the other hand, controls elements of the body at rest, such as rest and digestion. It’s believed that one system tends to be more dominant than the other, and thus a person’s metabolic functioning tends to vary.

2. The speed of cellular oxidation

Food oxidation involves how fast or how slow a person converts nutrients into energy. Thus, those who do it quickly require eating nutrients that are slower to degrade.

For example, due to the structure and type of bonds in proteins, their digestive process and oxidation is very slow. Meanwhile, there are people who oxidize food slowly, so they should eat more carbohydrates, as these are digested and oxidized quickly.

Types of metabolic typing diets

There are three types of diets according to the type of metabolism of the person. How are they identified? The authors of the book assess a number of characteristics related to nervous system dominance and oxidation rate.

Sugar, electrolyte, renal, and liver function tests are also performed. Blood and urine tests may be included for a more complete diagnosis.

1. The protein diet

This type of diet is designed for those who are rapid oxidizers or parasympathetic dominant. These are often people who experience constant hunger and tend to eat salty and fatty foods. In addition, they tend to fail with low-calorie diets and are nervous, anxious, and lethargic.

Through this dietary model, an intake of up to 40% protein, 30% carbohydrates, and 30% fat is proposed. The recommended foods include the following options:

• Poultry meats
• Offal
• Beef
• Fish and seafood
• Whole milk
• Cream
• Eggs
• Cheese

2. Carbo diet

The carbo diet is indicated for people who are slow oxidizers and sympathetic dominants. It’s believed that those who belong to this group depend on caffeine and tend to have a weakness for sweet foods. In addition, their appetite is reduced and they have problems controlling their weight.

In this case, an intake of about 60% carbohydrates, 20% protein, and 20% fat is suggested. However, the consumption of refined carbohydrates is limited. Instead, some indicated foods are the following:

• Fruits
• Vegetables
• Legumes
• Whole grains
• Chicken, turkey, fish, and seafood (as a source of protein)

3. Mixed diet

The mixed diet is indicated in those who don’t have a fast metabolism, but not a slow one, either. There is a tendency to consume sweet foods and their appetite is moderate. In addition, they tend to be anxious, nervous, and tire easily.

In general terms, it proposes an equal consumption of complex carbohydrates, fats, and proteins. However, proteins and fats may predominate.

What do experts think about the metabolic typing diet?

The creators and followers of the metabolic typing diet claim a weight loss of up to 10 pounds in one month. However, there are no studies to support this claim. So far, there are only anecdotal data on its alleged effects.

This is not to mention that health professionals agree that such rapid weight loss is unsustainable and untenable. Other experts also say that when weight is lost quickly, the metabolism also slows down. Therefore, the recovery of the lost weight occurs in a short time.

However, the Department of Agriculture (USDA) suggested an amplitude in the ranges of macronutrients, so that they are as follows:

• Protein: 10 to 35%
• Fats: 20 to 35%
• Carbohydrates: from 45 to 65 % for carbohydrates

According to this, significant differences can be noticed with the protein diet of the metabolic typing plan. Meanwhile, the carbo-type diet is within the recommended limits, while the mixed type is at a higher percentage of protein and fat.

The USDA also recommends calorie counting to promote weight loss. This is contrary to the recommendation of Dr. Wolcott, who sees no calorie counting as an advantage. The author of metabolic typing claims that the person will not be hungry between meals. But is this totally true?

It should also be kept in mind that if there are special health conditions, it’s essential to consult a doctor first before starting this dietary model.

In particular, diabetic patients should be careful, since the diet is key to controlling blood sugar levels. In this regard, a team of scientists determined that low-carbohydrate diets favor blood sugar control in type 1 diabetes.

The benefits of the metabolic typing diet

The metabolic typing diet is a personalized diet plan that takes into account the individual’s preferences and needs. It also limits the consumption of those carbohydrate sources that have high caloric values and almost no vitamin and mineral intake.

In summary, its benefits include the following:

• Weight loss
• Control of high glucose levels (depending on the type of diet chosen)
• The prevention of chronic diseases

The cons of the metabolic typing diet

Despite being a dietary model that promotes a healthy lifestyle, there’s still a lack of scientific support to corroborate its effectiveness and safety. A study that compared the results of the questionnaire applied to this diet with laboratory tests related to metabolism did not find any link.

On the other hand, the protein diet plan may increase the consumption of saturated fat related to the risks of heart disease and cardiovascular accidents. A lack of balance is also observed in the carbo and mixed diets. Some dietary imbalances can also lead to type 2 diabetes and obesity.

So does it really work?

It’s true that the metabolic typing diet is one of the most personalized diets when it comes to indicating the consumption of certain foods according to the type of metabolism. It’s also true that it evaluates some personality characteristics related to the dominant nervous system and that can affect the results of the diet.

However, the scientific literature doesn’t offer major studies that show the optimization of this type of diet to lose weight without any risk. People with certain health conditions should consult with their physician and a nutritionist before trying it. More research needs to be done in this regard.