What makes a diet actually healthy?

Our diets are one of the topmost factors when it comes to health risks. There is strong evidence that a healthy diet can help lower a person's risk of cardiovascular diseases and dementia . Modeling studies suggest eating healthily could even help prolong a person's life span .

Recent research has heralded several different diets as "healthy," suggesting that they bring cardiovascular, metabolic and brain health benefits. These include: Mediterranean diets, the MIND diet , and the DASH diet .

But what elements do all of these diets have in common, and what makes a diet, any diet, healthy?

A joint statement recently published by the World Health Organization (WHO) and the Food and Agriculture Organization (FAO) of the United Nations (UN) has sought to outline the "dos" and "don'ts" of healthy dietary habits.

It offers an overview of what nutrients are essential, what the best sources for those nutrients are, how many calories each of these nutrients should account for, and which foods a person would do best to avoid.

Additionally, two registered dietitian nutritionists (RDNs), not affiliated with the WHO or the FAO, have spoken to Medical News Today to explain the building blocks behind a truly healthy diet.

The recent WHO and FAO statement notes that carbohydrates are an essential part of a person's diet, explaining that they "provide the primary energy source for the body."

According to the report, carbs should make up 45% of total daily calories at a minimum, and no more than 75% of daily calories.

The best sources of carbs are:

And an adult's daily intake of fruit and vegetables should be at least 400 grams.

Michelle Routhenstein, MS, RD, CDCES , a preventive cardiology dietitian at EntirelyNourished, echoed this advice, telling MNT that:

"Carbohydrates are an essential macronutrient, serving as the brain's primary source of fuel. Adults need at least 130 grams of carbohydrates daily to support proper brain function. The best sources of carbohydrates are complex carbs, which are found in foods like whole grains, legumes, vegetables, low-fat dairy, and nuts and seeds."

"These foods provide not only energy but also important nutrients like potassium , magnesium , and chromium , which support heart health and help regulate blood sugar levels ," she further explained.

Fiber — also a type of carb — is important, too, and the joint statement advises that an adult should consume at least 25 grams of "naturally occurring dietary fiber" per day.

Speaking to MNT, Molly Rapozo, MS, RDN, CD , a registered dietitian nutritionist and senior nutrition and health educator at the Pacific Neuroscience Institute at Providence Saint John's Health Center in Santa Monica, CA, explained that "fiber is a part of plants that isn't fully digested; instead it moves through our bodies picking up stray fats and sugars, feeding the healthy bacteria in our gut, and removing toxins with regular bowel movements."

According to her, "a diet adequate in fiber [content] can help reduce the risk of heart disease and type 2 diabetes ."

Some good sources of dietary fiber are vegetables, fruit, whole grains, legumes, nuts, and seeds.

While many people may think of fats as unhealthy, the statement notes that "fat is an essential nutrient for proper functioning of cells in the body, and two fatty acids — linoleic acid and [alpha]-linolenic acid — can only be obtained from the diet."

Linoleic acid is an omega-6 fatty acid , while alpha-linolenic acid is an omega-3 fatty acid . Walnuts, sunflower seeds, and almonds are all good sources of omega-6, and fatty fish like tuna and salmon are a source of omega-3.

However, alpha-linolenic acid is derived from plant foods instead, especially rapeseed and walnuts.

According to the joint statement, in adults, 15–30% of daily calories should come from fats, primarily unsaturated fatty acids, such as those named above.

Routhenstein explained for MNT that "fats are necessary for hormone production, brain function, and to absorb fat-soluble vitamins and certain classes of antioxidants ."

"Choosing heart-healthy unsaturated fats like [those obtained from] avocados, nuts, and seeds protect[s] our heart health and help[s] to support healthy blood pressure and cholesterol levels," she further advised.

"Proteins provide the building blocks for much of the structural elements of the body, such as muscle, as well as functional molecules such as hormones and enzymes," the joint statement notes.

It advises that 10–15% of daily calories should come from proteins, and that these can be obtained from a mix of animal and plant sources.

However, it also notes that plant protein sources may be more beneficial for the cardiovascular and metabolic health of adults.

Rapozo explained that:

"Proteins are the building blocks for muscles, enzymes, and important hormones in our bodies. Older adults have additional protein needs to maintain muscle mass and strength, as well as bone health, immunity, and more. Protein needs vary; however, research shows it should be over the [United States] recommended dietary allowance of 0.8 [grams per kilogram] of body weight."

"Most healthy older adults — an exception being those with kidney disease — should consume 1 to 1.2 grams of protein per kilogram of body weight daily," she advised. "That's 68–82 grams for a 150-pound person."

Rapozo also noted that "this daily total should be broken up throughout the day, since we become less efficient at processing protein as we age," and suggested that a person should aim for 25–30 grams of protein per meal.

As for the best protein sources, she recommended:

She also advised that "cow, soy, or pea-based milks all contain protein, while many nut milks are not a good source."

The joint statement further notes that sodium — that is, salt — is an essential mineral, and thus should feature in our diets in moderate quantities.

At "high intakes [it] is associated with increased blood pressure which can lead to cardiovascular disease," it cautions. Thus, an adult should have no more than 2 grams of sodium per day, "corresponding to 5 grams of table salt."

The joint WHO and FAO statement further warns that "free sugars are not essential nutrients and [their] intake should be restricted to less than 10% of daily energy intake," noting that it is even better if under 5% of calorie intake comes from sugars.

Ultra-processed foods — described as foods that have undergone industrial processing "that alters the structure of the original food ingredients" — tend to contain high amounts of added salt and sugar, as well as substances such as flavor enhancers.

High consumption of ultra-processed foods, such as fast foods, has been linked to accelerated biological aging , a heightened risk of cognitive decline and stroke , and dozens of other health problems .

For this reason, the WHO and FAO advise against these types of foods. Nutritionists fully agree with this assessment, based on all the evidence available.

Rapozo said that if someone is unsure whether or not a food product counts as "ultra-processed," they should "read ingredient labels to help avoid [...] additives" like "artificial flavors and colors, sweeteners, hydrogenated oils, preservatives, and other manufactured additives."

She noted:

"Ask yourself if you can find these ingredients in your own kitchen or [if] they sound more like a chemical concoction? Ultra-processed ingredients may be found in chicken nuggets, frozen meals, hot dogs, packaged soups, soft drinks, breakfast cereals, as well as salty or sweet snacks like chips, crackers, and cookies."

Increasing evidence suggests that red meat contributes to colorectal and other types of cancer , increases the risk of type 2 diabetes , causes cardiovascular problems , and may even contribute to dementia .

"In adults, high intakes of red meat are associated with increased risk of several diseases and evolving evidence suggests that consumption of processed red meat, even at low levels, may have negative health consequences," reads the statement.

However, in Routhenstein's view, "when it comes to maintaining a healthy diet, it's more important that you focus on what you can include rather than focusing on what to avoid."

Rapozo agreed, advising that we tweak our existing diets in ways that are guaranteed to make them healthier:

"We can modify our diets to improve brain health by including vegetables, fruit, starches — such as whole grains, legumes, and potatoes — as well as lean protein, fatty fish, and plant fats such as nuts, seeds, avocado, olives, and olive oil. Eat less highly processed snack foods, fatty meats including bacon and sausage, sugar, and other refined carbohydrates."