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Dieting can be overwhelming. With new research constantly emerging, new diets seemingly popping up every week, and experts regularly claiming to have discovered the magic bullet to weight loss or nutrition, it’s difficult to even keep track of what’s out there these days, let alone determine which type of diet is best for you.

Physician Peter Attia has recognized this problem and attempted to simplify the process of understanding how diets work by using a basic nutritional framework that consists of three parameters:

• Dietary restriction: what you eat or don’t eat; in other words, if you’re focusing on only eating certain types of foods while avoiding other types, the diet would fall into this category


• Caloric restriction: how much you eat; this means counting the number of calories you consume and aiming for a specific target range


• Time restriction: when you eat or don’t eat; intermittent fasting, in which you only eat during a predetermined period each day and fast for the remainder, is the best example of a time–restrictive diet; we’ll explain this in more detail later

In Dr. Attia’s framework, each of these restrictions represents a lever that be plotted on an x–y–z axis. If you eat whatever you want, whenever you want, and as much as you want, you’re not pulling any of these levers. Instead, you’re following what’s called the standard American diet, which consists of lots of sugar, refined carbohydrates, saturated and trans fats, and is associated with high rates of obesity, diabetes, and other health issues. To break out of the standard American diet, Attia recommends pulling at least one of these levers. Pulling two, or possibly three, is even better.

Just about every diet that has ever been developed is structured on pulling one or more levers by regulating what, how much, and/or when you eat. All diets claim to help individuals lose weight or improve other aspects of their health by adhering to these restrictions, and many do have the potential to be beneficial—so long as it’s followed on a long—term basis.

Now that you have a general understanding of this framework, we’d like to describe a few of the most popular diets out there currently and explore what restrictions they recommend and the health benefits associated with each one.

Vegan and vegetarian diets are similar, but there is one key difference between them. A vegan diet consists only of plant–based foods and no foods derived from animals whatsoever. A vegetarian diet, on the other hand, does not include any meat, but may include other animal products like eggs (ovo vegetarian) or dairy (lacto vegetarian). Pesco vegetarians eat seafood, which doesn’t technically fit the definition of vegetarian, but oftentimes they are still classified together.

As you can see, vegan and vegetarian diets clearly pull on the dietary restriction lever of Attia’s nutrition framework. They do this by avoiding consumption of meat and possibly other animal–based products (depending on the specific type of diet). Vegans and vegetarians may also do indirectly do some caloric restriction by eating less high–calorie foods, but this depends largely on their food choices within each diet. Health benefits that have been identified with these diets include the following:

• A vegan diet can lower high cholesterol levels, mainly by eliminating lots of saturated fats and completely eliminating dietary cholesterol that’s only found in animal products


• Vegan diets are also associated with has anti–inflammatory effects in patients with heart disease and have been found to improve lipid and glycemic control in type 2 diabetics, which are two important parameters for these patients


• A vegetarian diet reduces the risk for heart disease and death related to heart issues


• Caution: a vegan or vegetarian diet isn’t automatically healthy, since potato chips, soda, and vegan ice cream all technically fit this classification

The ketogenic diet—or keto for short—places a strong emphasis on rich sources of fat (like meat and dairy), while limiting the consumption of foods high in carbohydrates (like fruit, whole grains, beans, and some vegetables). Moderate servings of protein are also allowed, but fats account for most of the calories consumed.

As with the vegan and vegetarian diets, the keto diet also pulls the dietary restriction lever by limiting the amount of carbs and protein while focusing on lots of fats. If the ketogenic diet is being followed for the primary purpose of losing weight, it can also pull the caloric restriction lever, but this is not always the case. Some of the health benefits associated with this diet include the following:

• Reduces blood pressure


• Helps with weight loss


• Improves lipid levels and has a positive impact on other markers that are associated with heart disease


• Caution: people on the keto diet are more prone to gain back weight than others because it can be difficult to stick to in the long term

One of the most rapidly emerging dietary trends is intermittent fasting, which involves only consuming meals within a strictly defined period. The most popular variations are the 16/8, 18/6, and 20/4 time–restricted feedings. This means an individual will fast for 16 hours and then eat only within an 8–hour “nutritional window” (or 18 hours of fasting followed by 6 hours of eating, etc.). A more aggressive approach includes alternating a 24–hour fasting period with a 24–hour eating period, two or three times a week. During eating periods, individuals do not have to be selective about what they eat, but healthy foods will lead to better results.

Intermittent fasting is clearly different from the other diets in that it focuses almost exclusively on pulling the time restriction lever. Some individuals who follow intermittent fasting will combine it with some other diet to also the types of foods they consume, but this is not a requirement. Intermittent fasting has been associated with several health benefits, including the following:

• Reduces blood pressure and prevents hypertension


• Can lead to weight loss


• Improves glucose metabolism and increases sensitivity to insulin in diabetic patients


• Caution: intermittent fasting can be difficult to sustain long–term, and it may also lead to negative side effects like mood swings, chronic tiredness, headaches, dizziness, and nausea; it’s also not recommended for those with hormonal imbalances and pregnant and breastfeeding women

Each diet clearly has some attractive qualities and could be good for your overall health if done properly. So ultimately, if you’re thinking about trying a new diet, the main question you should be asking yourself is this: which one can I stick with in the long term. Most diets fail because dieters are only able to maintain the restrictions for a few weeks or months. But enacting real change requires adopting a diet that you can maintain for the long haul, at which point it transitions from a “diet” to just the way that you eat.

Disclaimer: Physical therapists are not licensed to provide nutrition recommendations. This post is intended for informational purposes only.