Protein, fats, carbohydrates, fiber, vitamins, minerals, calories and food composition explained with practical context.
A normal serving of potatoes, beans, some cooked greens, fish, yogurt, or avocado can provide several hundred milligrams of potassium. Ranking foods by the amount people actually eat can look very different from a per-100-gram table.
Seeds are among the most concentrated magnesium sources, especially pumpkin and chia seeds, but an everyday diet can add substantial amounts through nuts, beans, whole grains and leafy greens. One ounce of pumpkin seeds provides about 156 mg.
Oranges are a good source of vitamin C, but they are not the champion. Red bell pepper, kiwi and several other fruits and vegetables can provide as much or more per serving, and prolonged storage or cooking can reduce some of the vitamin.
Oysters and liver stand out among animal foods, while beans, tofu, seeds and fortified foods can also provide substantial iron. The useful comparison is not just milligrams on a chart: serving size and the difference between heme and nonheme iron matter too.
Yogurt, milk, cheese, sardines with edible bones and tofu made with calcium salts can each provide roughly 250–400 mg of calcium in a normal serving. Seeds and some greens contribute too, but serving size and absorption make per-100-gram rankings misleading.
Chia, flax and walnuts are concentrated sources of the plant omega-3 ALA, while salmon, herring, sardines and mackerel provide mostly EPA and DHA. They belong to the same fatty-acid family but are not nutritionally interchangeable, so one combined ranking can mislead.
“Healthy fats” usually means prioritizing monounsaturated and polyunsaturated fats over saturated and trans fats. Olive oil, nuts, seeds, avocado and fatty fish are common sources, but all fats still provide about 9 calories per gram.
Saturated, monounsaturated and polyunsaturated fats are families of fatty acids with different chemical structures. In practical nutrition, the main distinction is that monounsaturated and polyunsaturated fats are generally favored, while saturated fat is limited and preferably replaced with unsaturated fat.
Nuts are high in calories because they pack a lot of fat into very little water: a 1-ounce serving usually provides about 155–200 calories. That does not make them nutritionally poor; most of their fat is unsaturated, and the same handful also provides protein, fiber, vitamins and minerals.
Nuts are calorie-dense, but that does not mean they automatically cause weight gain. Controlled trials have not found a meaningful increase in body weight when nuts are added to eating patterns; the practical question is how much you eat and what the nuts replace.
Avocado provides about 160 calories per 100 g — roughly three times the calories in an apple or orange by weight. That does not mean avocado automatically causes weight gain; portion size and total energy balance matter.
Most of the fat in avocado is monounsaturated, especially oleic acid. It also contains smaller amounts of polyunsaturated and saturated fat. Calling it a source of “healthy fat” refers mainly to that fatty-acid profile and the whole-food matrix, not to an absence of calories.