5 principles of a healthy diet

What's the healthiest way to eat? It depends on who you ask. Many medical and nutrition experts claim to know the "perfect" way to eat for health, yet some of these dietary advocates disagree with each other in some fundamental ways. So, who's right … and who's wrong?

While details may vary from diet to diet, all healthy eating plans have these five principles in common:

1. Lots of plants. Plant foods — vegetables, fruits, legumes, whole grains, nuts, and seeds — offer a wealth of vitamins and minerals, as well as fiber and healthful compounds called phytochemicals (literally "plant chemicals," natural substances in plants that offer humans a range of health benefits, including antioxidant, anti-inflammatory, and even anticancer activity). At the same time that many plant foods are high in nutrients, they are relatively low in calories. The combination of high nutrient content and low calories — a quality known as nutrient density — means that a plant-heavy diet can be good for both health and weight loss. Because people often underestimate how large their portions of fruits and vegetables should be, Harvard nutritionists devised the Harvard Healthy Eating Plate to provide a graphic representation of a healthy dinner. Fully half the plate contains produce.

2. Adequate protein. Abundant research shows it's important to eat enough protein, but there are many ways to get that protein, and some are more healthful than others. People who limit how much meat they eat tend to have lower risks for chronic diseases. Plant protein sources (beans, lentils, soy foods, nuts, seeds) and seafood offer the most health benefits. Getting enough protein, along with physical activity, is important for staying strong, healthy, and independent.
3. Minimally processed foods. A 2019 National Institutes of Health study definitively showed that eating a diet high in ultra-processed foods causes weight gain and unhealthy shifts in blood sugar and blood cholesterol. For the healthiest diet, rely as much as possible on whole foods (that is, unprocessed foods, such as broccoli, apples, and almonds) and minimally processed foods (such as plain yogurt, canned tuna, and natural peanut butter). Processing tends to strip away nutrients while adding extra fats, sugars, and sodium, not to mention other additives and preservatives.
4. Limited saturated fats, added sugars, and sodium. The U.S. government's Dietary Guidelines for Americans recommend limiting saturated fat intake to less than 10% of daily calories. The same goes for added sugars (sugars added during processing). If you have a 2,000-calorie-a-day diet, that means that no more than 200 calories a day should come from added sugars. As for sodium, keep it below 2,300 milligrams (mg) per day. The average American consumes more than 3,400 mg per day.
5. Balance and variety. To meet nutrient needs, it's important to choose a variety of nutrient-dense foods across and within all food groups. Choosing nutrient-dense foods helps you get the nutrients you need without taking in too many calories.

While everyone needs carbohydrates, fat, and protein, there is no magic ratio that you should be striving for, as long as you avoid extremes. To learn more about different diets from the experts at Harvard Medical School, check out The Diet Review, a Special Health Report from Harvard Medical School.

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