Many tried-and-tested diets have stood the test of time.

These include the Mediterranean diet, low-carb diets, the paleo diet, and whole-foods, plant-based diets.

These diets — and others shown to be healthy long term — share a few important similarities.

Here are 6 things that all successful diets have in common.

1. Low in Added Sugar

Added sugar is one of the unhealthiest aspects of the modern diet.

Though some people can tolerate moderate amounts of sugar without problems, most people are eating too much (1).

When you eat too much fructose — one of the main forms of sugar — it overloads your liver, which is forced to turn it into fat (2, 3).

Part of the fat gets removed from your liver as very low-density lipoprotein (VLDL) cholesterol — raising blood triglycerides — but some of it remains in your liver (4, 5).

In fact, excessive fructose intake is believed to be a major driver of nonalcoholic fatty liver disease (6, 7).

It is also associated with many other conditions, including obesity, type 2 diabetes, and heart disease (8, 9, 10, 11).

What’s more, sugar provides empty calories, as it supplies many calories but virtually no essential nutrients.

Most experts agree that excessive intake of added sugar is harmful. Therefore, most successful diets make it a priority to cut back on added sugar.

SUMMARY There is universal agreement that a high intake of added sugar is unhealthy, and most successful diets recommend limiting it.

2. Eliminate Refined Carbs

Refined carbs — which are sugar and processed starchy foods, including grains, that have had most of the fiber removed — are another ingredient that nutrition experts agree is unhealthy.

The most common refined carb is wheat flour, which is consumed in massive amounts in Western countries.

As refined grains are made by pulverizing whole grains and removing the bran and endosperm — the fibrous and nutritious parts — refined starch provides many calories but almost no essential nutrients.

Without the fiber of the whole grain, starch can cause rapid spikes in blood sugar, leading to cravings and overeating a few hours later when blood sugar comes crashing down (12, 13).

Studies link refined carbs to various metabolic conditions, including obesity, type 2 diabetes, and heart disease (14, 15, 16, 17, 18).

Though some diets — like paleo and low-carb — eliminate grains altogether, all successful diets at least emphasize limiting refined grains and replacing them with their whole, healthier counterparts.

SUMMARY All successful diets eliminate refined grains like wheat flour, while some diets like paleo and low-carb ban grains altogether.

3. Avoid Vegetable Oils High in Omega-6 Fat

Though vegetable oils have been around for thousands of years, mass production of refined oils didn’t start until the early 20th century.

These include soybean oil, canola oil, corn oil, cottonseed oil, and a few others.

Some people are concerned about the high content of polyunsaturated omega-6 fatty acids in some vegetable oils. Scientists have pointed out that most people may be eating too much omega-6 fat (19).

Omega-6 fat may cause LDL (bad) cholesterol to become oxidized more easily and contribute to endothelial dysfunction — two key steps in the heart disease process (20, 21, 22, 23, 24).

Still, whether they cause or prevent heart disease is controversial. Some observational studies indicate protective effects, but many controlled trials suggest that they may be harmful (25, 26, 27, 28).

Other studies observe that linoleic acid — the most common omega-6 fatty acid — does not increase blood levels of inflammatory markers (29, 30).

While more research is needed before any solid conclusions can be reached, most scientists agree that people’s intake of omega-6 has increased significantly in the past century.

If you’re concerned about omega-6, limit your intake of vegetable oils like soybean oil and canola oil. Instead, choose olive oil and other oils low in omega-6.

SUMMARY Many diets encourage lower intake of omega-6-rich vegetable oils like soybean or canola oils. Still, it remains unknown whether or not these oils are harmful.

4. Eliminate Artificial Trans Fats

Trans fats are usually made by hydrogenating vegetable oils, which makes them solid at room temperature and increases shelf life (31).

Numerous studies link trans fats to increased inflammation and heart disease (32, 33).

The evidence is so strong that many countries have limited or banned the use of trans fats in foods.

In the United States, the federal ban of trans fats went into effect in June 2018, though already manufactured products can still be distributed until January 2020, or in some cases 2021 (34).

Plus, foods are labeled as having 0 grams of trans fat if they contain less than 0.5 grams (35).

SUMMARY Trans fats are made by hydrogenating vegetable oils. Many studies show a link to inflammation and conditions like heart disease. Its use has been limited or banned in many countries, including the United States.

5. High in Vegetables and Fiber

Many diets limit or eliminate certain foods.

For example, plant-based diets minimize or completely eliminate animal foods, while low-carb and paleo diets eliminate grains.

However, though some successful diets — like the low-carb way of eating — may restrict carb-rich, starchy vegetables, all healthy diets include plenty of veggies in general.

It’s universally agreed upon that vegetables are healthful, and numerous studies support this by showing that vegetable consumption is linked to reduced disease risk (36, 37, 38).

Vegetables are high in antioxidants, nutrients, and fiber, which aids weight loss and feeds your friendly gut bacteria (39, 40, 41).

Most diets — even low-carb ones — also include fruit to some degree.

SUMMARY All successful diets emphasize eating plenty of vegetables and — in most cases — fruit. These foods are high in antioxidants and healthy prebiotic fibers.

6. Focus on Foods Instead of Calories

Another thing that successful diets have in common is that they emphasize the importance of whole, single-ingredient foods rather than calorie restriction.

Though calories are important for weight management, simply restricting them without regard to the foods you eat is rarely effective in the long term.

Instead of trying to lose weight or restrict calories, make it your goal to nourish your body and become healthier.

SUMMARY Most successful diets emphasize a lifestyle change that includes whole foods — and let weight loss follow as a natural side effect.

The Bottom Line

Most healthy diets — like the Mediterranean diet, low-carb diets, the paleo diet, and whole-foods, plant-based diets — have a few things in common.

Most importantly, they focus on whole foods and encourage people to limit their intake of processed food, trans fat, added sugar, and refined carbs.

If you wish to improve your health, consider replacing some of the processed foods you’re eating with whole foods, including vegetables, fruits, and whole grains.