There are dozens of named diets, but most fall into a handful of categories based on what they emphasize or restrict: plant-based diets, low-carbohydrate diets, heart-healthy dietary patterns, time-restricted eating, and ancestral or elimination-style diets. Some are designed for managing a health condition, others for weight loss, and others reflect ethical or environmental choices. Here’s how the major types work and what sets them apart.
Heart-Healthy Diets
Two dietary patterns dominate the conversation around cardiovascular health: the Mediterranean diet and the DASH diet. Both consistently rank among the top overall diets evaluated by expert panels each year, and both have strong clinical evidence behind them.
The Mediterranean diet emphasizes vegetables, fruits, whole grains, legumes, nuts, olive oil, and fish, with moderate amounts of poultry and dairy and limited red meat. A landmark trial called PREDIMED was actually stopped early because participants on the Mediterranean diet (supplemented with olive oil or nuts) showed such a clear reduction in cardiovascular events compared to a low-fat diet that it was considered unethical to continue. A meta-analysis of over 50,000 people found the diet significantly reduced the risk of metabolic syndrome and improved waist circumference, blood sugar, blood pressure, and cholesterol levels. Long-term adherence also lowers markers of inflammation in the body.
The DASH diet (Dietary Approaches to Stop Hypertension) was specifically developed to lower blood pressure. It looks similar to the Mediterranean diet in many ways, with a heavy emphasis on fruits, vegetables, and whole grains, but it places a specific cap on sodium: no more than 2,300 milligrams per day, with even greater blood pressure benefits at 1,500 milligrams. The DASH diet ranks as the second-best overall diet and the top heart-healthy diet in the 2025 U.S. News & World Report rankings, which are evaluated by 69 expert panelists including doctors, dietitians, and nutritional researchers.
Low-Carbohydrate and Ketogenic Diets
Low-carb diets reduce carbohydrate intake to varying degrees, replacing those calories primarily with fat, protein, or both. The spectrum ranges from moderate low-carb approaches (roughly 60 grams of carbohydrates per day in many studies) to the strict ketogenic diet, which typically limits carbs to 20 to 50 grams per day, or about 5 to 10 percent of total calories.
The ketogenic diet works by pushing the body into a metabolic state called ketosis, where it burns fat for fuel instead of glucose. A well-formulated version gets most of its calories from fat, with moderate protein (roughly 1 to 1.5 grams per kilogram of body weight) and very few carbs. Several studies have shown that people on ketogenic diets tend to eat fewer calories spontaneously, likely because fat and protein are more satiating. In a 12-week trial of overweight adults, those on a carb-restricted plan (12% carbs, 59% fat, 28% protein) saw greater reductions in triglycerides and increases in HDL (“good”) cholesterol compared to a low-fat group.
The Atkins diet is probably the most well-known branded low-carb plan. It starts with a very strict induction phase similar to keto, then gradually reintroduces carbohydrates. South Beach is another variation that focuses more on choosing “good” carbs and fats rather than cutting carbs to extreme levels.
Plant-Based Diets
Plant-based eating exists on a spectrum, and the differences between the labels matter when it comes to nutrition.
- Vegan: No food of animal origin at all. No meat, dairy, eggs, or honey.
- Vegetarian: No meat or fish, but dairy and eggs are typically included. Variations like lacto-vegetarian (dairy but no eggs) and ovo-vegetarian (eggs but no dairy) exist.
- Flexitarian: Mostly plant-based, with small amounts of meat. Definitions vary, but researchers generally describe it as eating meat no more than a few times per week, or consuming roughly 350 grams (about 12 ounces) or less of meat per week.
The most common nutritional gap across all plant-based diets is vitamin B12, which is found almost exclusively in animal foods. In one cross-sectional study, none of the dietary groups (vegan, flexitarian, or omnivore) reached the recommended daily intake of 4 micrograms, but vegans had the lowest levels by far. The contribution of plant foods to B12 is essentially negligible, so supplementation is strongly recommended for vegans and worth considering for flexitarians as well.
Iron is another concern, particularly for women. In that same study, 67% of women eating a flexitarian diet and 61% of vegan women showed signs of iron deficiency or pre-latent iron deficiency, compared to 54% of women eating an omnivorous diet. Calcium and zinc are also nutrients to watch on a fully vegan diet.
Intermittent Fasting
Intermittent fasting isn’t really about what you eat. It’s about when you eat. The three most common protocols are time-restricted feeding, the 5:2 diet, and alternate-day fasting.
Time-restricted feeding (often called 16:8) means eating within a set window each day, typically 8 hours, and fasting for the remaining 16. You eat whatever you normally would during the feeding window. The emphasis is on the daily rhythm, not on calorie counting. Some people use tighter windows of 6 or even 4 hours.
The 5:2 diet takes a different approach: you eat normally five days a week and dramatically reduce your calorie intake on two days, typically to about 50% of your normal intake or roughly 500 to 600 calories. Those two fasting days can be consecutive or spread throughout the week.
Alternate-day fasting is the most intensive version, alternating between regular eating days and fasting or very-low-calorie days. All three patterns create a calorie deficit over time, but they get there through different rhythms, and people tend to stick with whichever pattern fits their lifestyle most naturally.
Ancestral and Elimination Diets
Some diets are built around the idea of returning to a more “natural” way of eating by eliminating modern processed foods and, in some cases, entire food groups.
The Paleo diet models itself after what humans presumably ate before agriculture. It allows meat, fish, poultry, eggs, vegetables, fruits, and nuts. It excludes dairy, grains, legumes, potatoes, and all refined or artificial products, including oils like olive oil. The philosophy is that our bodies haven’t evolved to process foods that appeared after the agricultural revolution.
The carnivore diet takes restriction much further: only meat, poultry, fish, eggs, and dairy are allowed. Every plant food is off the table, including vegetables, fruit, grains, legumes, nuts, and seeds. This is one of the most restrictive dietary patterns in common practice, and it eliminates virtually all dietary fiber and many vitamins typically obtained from plant sources.
The Whole30 is a 30-day elimination protocol that removes sugar, alcohol, grains, legumes, soy, and dairy, then reintroduces them one at a time. It’s designed less as a permanent diet and more as a diagnostic tool to identify which foods cause digestive issues or other symptoms.
Anti-Inflammatory Diets
Anti-inflammatory diets overlap heavily with Mediterranean-style eating but frame food choices specifically around reducing chronic inflammation, which plays a role in heart disease, diabetes, and many autoimmune conditions. The core of the approach is high consumption of fruits, vegetables, whole grains, legumes, fatty fish, nuts, and olive oil, while limiting red meat, refined carbohydrates, and alcohol.
The evidence for specific foods is surprisingly detailed. A systematic review found that swapping refined grains for whole grains significantly lowered C-reactive protein, a key marker of inflammation in the blood. Almond consumption, particularly at doses under 60 grams per day (a small handful), reduced both CRP and another inflammatory marker called IL-6. Soy products have shown similar effects. Even fermented dairy products containing specific probiotic strains lowered CRP after just four weeks of daily use.
Weight Loss Diets
Many of the diets above can be used for weight loss, but some are designed specifically with calorie reduction as the primary mechanism. These include calorie-counting programs like Weight Watchers (now called WeightWatchers), which assigns point values to foods, and very-low-calorie diets that restrict intake to 800 calories or fewer per day under medical supervision.
The Dietary Guidelines Advisory Committee deliberately separates energy-restricted weight loss diets from broader dietary patterns in its research, because when calories are dramatically cut, it becomes difficult to tell whether health improvements come from the eating pattern itself, the calorie reduction, or the weight loss. This is worth keeping in mind when evaluating any diet that promises specific health benefits alongside rapid weight loss: the weight loss alone may be doing most of the work.
Choosing Based on Your Goals
The best way to think about diets is by what problem you’re trying to solve. If your priority is heart health or blood pressure, the Mediterranean and DASH diets have the deepest evidence base. If you’re focused on blood sugar control or want to reduce triglycerides, a well-formulated low-carb or ketogenic approach has shown measurable results. If you’re motivated by environmental or ethical concerns, plant-based diets at any level of strictness can work nutritionally, as long as you pay attention to B12, iron, and calcium. If your schedule makes traditional meal patterns difficult, intermittent fasting offers flexibility without requiring you to change what you eat.
Any diet that eliminates entire food groups carries a higher risk of nutritional gaps. The more restrictive the pattern, the more deliberate you need to be about supplementation and variety within whatever foods remain on the list. Vegan, carnivore, and strict Paleo diets all require this kind of intentional planning to avoid deficiencies over time.