The metabolic type diet is a pseudoscientific approach to nutrition that claims individuals have unique dietary needs based on their metabolic type. This system categorizes people into broad metabolic types based on visible symptoms related to the skin, eyes, and other body parts. Understanding your metabolic type, whether you're carb-efficient or fat-protein efficient, can guide you toward a tailored diet and lifestyle for better health and well-being.
Origin and Development
Metabolic typing was introduced in the 1960s by William Donald Kelley, a dentist. Kelley advocated dietary choices based on the activity of one's sympathetic and parasympathetic nervous systems. In 1970, Kelley was convicted of practicing medicine without a license after diagnosing a patient with lung cancer using a fingerstick blood test and prescribing nutritional therapy. Despite this, he continued promoting the metabolic typing diet through the 1980s. The practice has been further developed by others, including Harold J. Kristal and William Wolcott.
Methods of Assessment
Some metabolic typing companies use blood and urine tests performed by reputable laboratories but interpret the results in an unconventional and medically questionable fashion. During a 1985 investigation into one such firm, an investigator sent two separate samples of his own blood and urine for analysis and received two drastically different "metabolic typing" reports and dietary plans.
Kelley's Classification of Metabolism
In his book, William Donald Kelley classified metabolism into three categories: fast, slow, and mixed oxidizers. The diet varies based on the rate of oxidization. Fast oxidizers, who process food quickly, are advised to rely more on a fat- and protein-efficient diet to manage hunger better. Slow oxidizers are recommended a carbohydrate-efficient diet, as eating too much protein or fat can cause abdominal pain.
The Three Types of Metabolism
Every person experiences the process of metabolism differently, with three distinct types categorizing the broad differences in metabolism, also known as somatotypes. These types impact how people convert, use, and store energy from food:
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- Endomorph
- Mesomorph
- Ectomorph
While each of these metabolism types has specific characteristics, most people can identify with one of these types or see themselves reflected as a combination of types.
Endomorph
Endomorph is the most common body type, with 70% of the population having some endomorph characteristics. This describes a body type characterized by having a larger bone structure and a higher percentage body fat. They often carry most of their weight in their lower body and can typically develop muscle tissue quite quickly, so they will have an easier time building strength. They tend to be efficient in nutrient storage and store fat easily. Metabolically, the endomorph metabolism is generally slower than the other two types, which makes it more difficult to lose weight, as their bodies are more biologically prone to holding on to excess fat. Also, these people may be more prone to sedentarism and fatigue easily because of excess weight.
Nutrition Advice: People with endomorphic bodies tend to be more sensitive to carbohydrates and insulin. Foods rich in carbohydrates release sugars rapidly into the bloodstream, causing blood sugar spikes and dips. The body is also more likely to turn these sugars into fat than burn them as energy. People following an endomorph diet may benefit most from foods that provide steady fuel without spiking blood sugar, such as complex carbs from vegetables and high-fiber grains, rather than simple or refined carbs like sugar and starches. They should aim to consume a diet rich in nutrient-dense foods, including lean quality protein, healthy fats (fish, nuts, avocado, and healthy oils), that will help hunger and energy levels without increasing blood sugar. There are a few specific diet plans that meet these nutritional guidelines, including paleo and keto diets, both focusing on low carbohydrate and high protein foods.
Exercise Tips: The American Council on Exercise (ACE) recommends that people with an endomorph body type follow “well-rounded” exercise routines that focus on both cardiovascular and strength training workouts. An endomorph body is well-primed to build and gain muscle quality. If you’re looking to build strength, moderate-to-heavy lifting that incorporates large muscle groups will give you the best results (deadlifts, squats, pushups). Cardiovascular exercises can help create a calorie deficit and potentially burn excess fat. Endomorphic body types respond well to a mix of high-intensity interval training (HITT) and steady-state training (SST) workouts. In HIIT, you will alternate between periods of very high-intensity exercise and low-intensity exercises. Try doing HIIT sessions 2-3 times per week. People with an endomorph body type can try doing 30-60 minutes SST 2-3 times per week (walking, jogging, and swimming).
Mesomorph
This body type is often described as a naturally athletic physique. Mesomorphs typically have an athletic, medium build with higher-than-average muscular development and relatively low body fat. Unfortunately, they also can gain fat easily, particularly in the lower body. Mesomorphs are strong, respond well to exercise (they can see quick changes and results when starting a new workout routine), and typically can eat a moderate amount of food relative to their activity level without gaining a lot of weight.
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Nutrition Advice: The best diet for a mesomorph will depend on an individual’s health or fitness goals. To maintain muscle mass and prevent body fat gain, the mesomorph diet should be a well-balanced diet. Since this body type tends to put on muscle quite easily, including a source of protein at each meal can help support the body’s natural inclination. Generally, they should focus on getting a healthy mix of complex carbs, lean proteins, fresh fruit and vegetables, and healthy fats. Make sure your carb intake is heavy on plants and high fiber. If weight loss if your goal, cut back processed foods, reduce portion sizes and calorie intake.
Exercise Tips: Mesomorphs respond favorably to just about any kind of exercise. To achieve a lean and muscle physique, it’s important to incorporate a relatively even mix of cardiovascular endurance and strength training into their workout routines. While mesomorph body types can see the most progress after weight and strength training workouts, it’s valuable to not forgo other types of exercise. Mesomorphs can also afford to do more functional and conditioning work. HITT training is a great option and might be particularly prevalent for a mesomorph trying to lose unwanted body fat. It’s encouraged to also get in flexibility or mobility training. Flexibility is all about recovery and making sure your body can perform at their optimum level.
Ectomorph
The ectomorph’s body frame is the smallest of the three body types and is characterized as thin and lean. Ectomorphs tend to have slender waists, narrow hips and shoulders, small joints, and long legs and arms. They typically have a low body fat percentage and low muscle mass. Metabolically, they have a faster metabolism, which means they tend to not gain weight or muscle easily. Since they burn calories quickly, ectomorphs might feel hungrier frequently, despite what, how much, or how often they eat.
Nutrition Advice: The key diet for an ectomorph body type is to still focus on eating a healthy, well-balanced diet rich in nutrients to provide the best fuel for the body. Because of the ectomorph’s fast metabolism, it may seem like they can eat whatever foods they want, but that doesn’t mean that they should eat everything. It can be beneficial for them to consume 5-6 small meals every few hours to help them stay feeling full and satisfied. Ectomorphs are often advised to increase their calorie and carbohydrate intake. Eating a great amount of complex carbohydrates from healthy whole grains and high-fiber foods can provide quick hits of energy that keep the body running well. If one is looking to build muscle mass, additional protein sources would be encouraged. They should also incorporate vegetables, fruits, and healthy fat sources like nuts and seeds. All of these food sources will help with weight gain and muscle building.
Exercise Tips: Ectomorphs are at a disadvantage when it comes to building muscle and toning the body with a thin frame, but it can be achieved by a dedicated training and nutrition plan. To build muscle mass, increase strength, and sculpt the body, a simple and consistent weight training routine should be their focus. Strength will happen most efficiently with slow, heavy weights and completing five sets of approximately 8-12 reps for each muscle group. Ectomorphs tend to excel in endurance-type activities, so It’s not surprised they may prefer cardio training instead of weightlifting. The key is to balance out the strength training with a couple of days of cardio to keep your heart in good shape.
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Metabolic Diets
Several diets fall under the umbrella of "metabolic diets," including the fast metabolism diet, high metabolism diet, metabolism miracle, and MD diet factor. These diets often emphasize reducing carbohydrate intake to lose weight, similar to the Atkins diet. However, they differentiate between complex carbohydrates (whole grains, oats, and brown rice) and refined carbs (processed breads, flours, and sugars). A common component of these diets is eating small meals throughout the day to help kick-start your metabolism.
Famous Metabolic Diets
- The Metabolic Typing Diet: Created by William Donald Kelley, this diet classifies metabolism as fast oxidizer, slow oxidizer, and mixed oxidizer, determined by the autonomic nervous system and oxidation rate. However, this diet has a host of issues starting from a vague categorization of Metabolic Type leading to a prescribed way of eating that has no scientific basis for weight loss.
- The Zone Diet: Developed by Dr. Barry Sears, the Zone Diet focuses on a specific ratio of macronutrients to reduce inflammation: 40% carbohydrates, 30% protein, and 30% fat.
- The Atkins Diet: Promoted by Dr. Robert Atkins, this diet emphasizes high fat and protein intake with limited carbohydrates.
Autonomic Nervous System and Cellular Oxidation
According to metabolic typing, two inherited factors determine your body’s metabolic rate:
- The rate of cellular oxidation: Cellular oxidation is the process your cells use to turn food into energy. Proponents of metabolic typing believe that some people oxidize food more quickly.
- The dominant autonomic nervous system: Your autonomic nervous system controls many of your background bodily functions: blood flow, breathing, heartbeat, digestion, and so on. Metabolic type dieters believe that, due to your parents’ genetics, your autonomic nervous system has one branch that’s stronger than the other.
Criticisms and Scientific Evidence
The major con of the metabolic type diet is that there’s no scientific research to back it up. Most nutrition experts agree that metabolic typing is inaccurate. So far, there’s been only one published study on metabolic typing. There was no correlation between the participants’ supposed metabolic type and what lab tests showed about their metabolism.
Practical Advice
Regardless of your metabolic type, metabolic typing recommends a whole-food-based diet that is high in vegetables and low in processed snacks and refined sugars. If you decide to try metabolic type dieting, pay attention to how you feel, and don’t be afraid to make changes if something isn’t working for you.