Nutrition glossary
What is diet quality?
Diet quality describes how healthy your overall eating pattern is: how much of your food comes from vegetables, fruit, whole grains, beans, nuts and other nourishing foods, and how much comes from added sugar, salt, processed meat and refined snacks. It's about the whole picture over weeks, not one meal or one nutrient.
What diet quality covers
Calories tell you how much energy you eat. Diet quality tells you what that energy brings with it. Most definitions look at a few things together:
- Adequacy: do you get enough protein, fibre, vitamins and minerals?
- Variety: do you eat a range of plant foods and protein sources, or the same few items every day?
- Balance: are your meals built around whole foods, with carbs, protein and fat in sensible proportions?
- Moderation: are added sugar, salt, saturated fat and alcohol kept to modest amounts?
Same calories, different quality
Here are two days, each around 1,800 kcal. Both could lead to the same weight change, but they are very different for your health.
| Meal | Lower-quality day | Higher-quality day |
|---|---|---|
| Breakfast | Sugary cereal with milk, glass of orange juice | Porridge with banana and a spoonful of peanut butter |
| Lunch | White bread ham sandwich, crisps, cola | Wholemeal wrap with chicken, hummus and salad; an orange |
| Snack | Chocolate bar | Greek yogurt and a handful of walnuts |
| Dinner | Frozen pepperoni pizza | Salmon, brown rice, broccoli and peppers cooked in olive oil |
| Rough result | Low fibre, high added sugar and salt, few vegetables | Plenty of fibre and protein, several portions of fruit and veg, little added sugar |
How diet quality is measured
Researchers turn diet quality into a score so they can compare groups of people and link eating patterns to health. The best-known scores include:
- Healthy Eating Index (HEI): a 0 to 100 score used in the US that measures how closely a diet matches the Dietary Guidelines for Americans.
- Alternative Healthy Eating Index (AHEI): developed at Harvard, it gives more weight to foods linked to lower risk of chronic disease, such as nuts, whole grains and healthy fats.
- Mediterranean diet scores: points for vegetables, fruit, legumes, fish and olive oil, and fewer points for red and processed meat.
- DASH scores: based on the DASH eating plan for blood pressure.
These scores differ in detail, but they reward mostly the same things. That's reassuring: there's broad agreement on what a good diet looks like, even among experts who argue about the finer points.
Why diet quality matters
In large long-term studies, people with higher diet quality scores tend to have lower rates of heart disease, type 2 diabetes and some cancers. These are observational studies, so they show links rather than proof, but the pattern is consistent across many countries.
Diet quality also affects how a diet feels day to day. Meals rich in fibre and protein are more filling, so a calorie deficit is easier to stick to. It's also why one "bad" meal isn't worth worrying about: what matters is your usual pattern.
Simple ways to improve yours
- Add one extra portion of vegetables or fruit a day before you think about cutting anything.
- Swap one refined grain for a whole one: brown rice for white, wholemeal bread for white, or oats for sugary cereal.
- Eat beans, lentils or chickpeas two or three times a week.
- Have oily fish, like salmon, sardines or mackerel, about once or twice a week if you eat fish.
- Cut back on sugary drinks and added sugar, and keep processed meat as an occasional food.
Common questions
What is the difference between diet quality and diet quantity?
Quantity is how much you eat, usually measured in calories. Quality is what the food is made of and what it gives your body. You can eat the right amount of poor-quality food, or too much of good-quality food, so both matter.
Which diet has the highest diet quality?
There isn't a single winner. The Mediterranean, DASH and well-planned plant-based diets all score well, because they share the same basics: lots of plants, whole grains, healthy fats and little processed food.
Can a low-carb or keto diet be high quality?
Yes, if it's built on vegetables, nuts, seeds, fish, eggs and olive oil rather than processed meat and cheese. But cutting out whole grains, beans and most fruit makes it harder to hit fibre targets, so it takes more planning.
Related
For the everyday basics, read healthy eating basics and the healthy eating hub. For diets that score well, see the Mediterranean diet and DASH diet. Related terms: macronutrients and glycemic index. Also see is there one best diet and how to choose a diet.