Nutrition is the study of nutrients in food, how the body uses them, and the relationship between diet, health, and disease.
Nutritionists use ideas from molecular biology, biochemistry, and genetics to understand how nutrients affect the human body.
Nutrition also focuses on how people can use dietary choices to reduce the risk of disease, what happens if a person has too much or too little of a nutrient, and how allergies work.
Nutrients provide nourishment. Proteins, carbohydrates, fat, vitamins, minerals, fiber, and water are all nutrients. If people do not have the right balance of nutrients in their diet, their risk of developing certain health conditions increases.
This article will explain the different nutrients a person needs and why. It will also look at the role of the dietitian and the nutritionist.
Macronutrients are nutrients that people need in relatively large quantities.
Sugar, starch, and fiber are types of carbohydrates.
Sugars are simple carbs. The body quickly breaks down and absorbs sugars and processed starch. They can provide rapid energy, but they do not leave a person feeling full. They can also cause a spike in blood sugar levels. Frequent sugar spikes increase the risk of type 2 diabetes and its complications.
Fiber is also a carbohydrate. The body breaks down some types of fiber and uses them for energ; others are metabolized by gut bacteria, while other types pass through the body.
Fiber and unprocessed starch are complex carbs. It takes the body some time to break down and absorb complex carbs. After eating fiber, a person will feel full for longer. Fiber may also reduce the risk of diabetes, cardiovascular disease, and colorectal cancer. Complex carbs are a more healthful choice than sugars and refined carbs.
Proteins consist of amino acids, which are organic compounds that occur naturally.
Some foods provide complete protein, which means they contain all the essential amino acids the body needs. Other foods contain various combinations of amino acids.
Most plant-based foods do not contain complete protein, so a person who follows a vegan diet needs to eat a range of foods throughout the day that provides the essential amino acids.
Fats are essential for:
- lubricating joints
- helping organs produce hormones
- enabling the body to absorb certain vitamins
- reducing inflammation
- preserving brain health
However, the type of fat a person eats makes a difference. Unsaturated fats, such as olive oil, are more healthful than saturated fats, which tend to come from animals.
Many people recommend consuming 2 liters, or 8 glasses, of water a day, but it can also come from dietary sources, such as fruit and vegetables. Adequate hydration will result in pale yellow urine.
Requirements will also depend on an individual's body size and age, environmental factors, activity levels, health status, and so on.
Micronutrients are essential in small amounts. They include vitamins and minerals. Manufacturers sometimes add these to foods. Examples include fortified cereals and rice.
The body needs carbon, hydrogen, oxygen, and nitrogen.
It also needs dietary minerals, such as iron, potassium, and so on.
In most cases, a varied and balanced diet will provide the minerals a person needs. If a deficiency occurs, a doctor may recommend supplements.
Here are some of the minerals the body needs to function well.
Potassium is an electrolyte. It enables the kidneys, the heart, the muscles, and the nerves to work properly. The 2015–2020 Dietary Guidelines for Americans recommend that adults consume 4,700 milligrams (mg) of potassium each day.
Too much may be harmful to people with kidney disease.
Avocados, coconut water, bananas, dried fruit, squash, beans, and lentils are good sources.
Sodium is an electrolyte that helps:
- maintain nerve and muscle function
- regulate fluid levels in the body
Too much can lead to high blood pressure, which increases the risk of cardiovascular disease and stroke.
Table salt, which is made up of sodium and chloride, is a popular condiment. However, most people consume too much sodium, as it already occurs naturally in most foods.
Experts urge people not to add table salt to their diet. Current guidelines recommend consuming no more than 2,300 mg of sodium a day, or around one teaspoon.
This recommendation includes both naturally-occurring sources, as well as salt a person adds to their food. People with high blood pressure or kidney disease should eat less.
The body needs calcium to form bones and teeth. It also supports the nervous system, cardiovascular health, and other functions.
Too little can cause bones and teeth to weaken. Symptoms of a severe deficiency include tingling in the fingers and changes in heart rhythm, which can be life-threatening.
Too much can lead to constipation, kidney stones, and reduced absorption of other minerals.
Current guidelines for adults recommend consuming 1,000 mg a day, and 1,200 mg for women aged 51 and over.
Good sources include dairy products, tofu, legumes,and green, leafy vegetables.
Phosphorus is present in all body cells and contributes to the health of the bones and teeth.
Too little phosphorus can lead to bone diseases, affect appetite, muscle strength, and coordination. It can also result in anemia, a higher risk of infection, burning or prickling sensations in the skin, and confusion.
Too much in the diet is unlikely to cause health problems though toxicity is possible from supplements, medications, and phosphorus metabolism problems.
Adults should aim to consume around 700 mg of phosphorus each day. Good sources include dairy products, salmon, lentils, and cashews.
Too little magnesium can eventually lead to weakness, nausea, tiredness, restless legs, sleep conditions, and other symptoms.
Too much can result in digestive and, eventually, heart problems.
Nuts, spinach, and beans are good sources of magnesium. Adult females need 320 mg of magnesium each day, and adult males need 420 mg.
Zinc plays a role in the health of body cells, the immune system, wound healing, and the creation of proteins.
Adult females need 8 mg of zinc a day, and adult males need 11 mg. Dietary sources include oysters, beef, fortified breakfast cereals, and baked beans. For more on dietary sources of zinc, click here.
Iron is crucial for the formation of red blood cells, which carry oxygen to all parts of the body. It also plays a role in forming connective tissue and creating hormones.
Too little can result in anemia, including digestive issues, weakness, and difficulty thinking. Learn more here about iron deficiency.
Too much can lead to digestive problems, and very high levels can be fatal.
Good sources include fortified cereals, beef liver, lentils, spinach, and tofu. Adults need 8 mg of iron a day, but females need 18 mg during their reproductive years.
The body uses manganese to produce energy, it plays a role in blood clotting, and it supports the immune system.
Too little can result in weak bones in children, skin rashes in men, and mood changes in women.
Too much can lead to tremors, muscle spasms, and other symptoms, but only with very high amounts.
Mussels, hazelnuts, brown rice, chickpeas, and spinach all provide manganese. Male adults need 2.3 mg of manganese each day, and females need 1.8 mg.
Too little copper can lead to tiredness, patches of light skin, high cholesterol, and connective tissue disorders. This is rare.
Too much copper can result in liver damage, abdominal pain, nausea, and diarrhea. Too much copper also reduces the absorption of zinc.
Good sources include beef liver, oysters, potatoes, mushrooms, sesame seeds, and sunflower seeds. Adults need 900 micrograms (mcg) of copper each day.
Too much selenium can cause garlic breath, diarrhea, irritability, skin rashes, brittle hair or nails, and other symptoms.
Adults need 55 mcg of selenium a day.
Brazil nuts are an excellent source of selenium. Other plant sources include spinach, oatmeal, and baked beans. Tuna, ham, and enriched macaroni are all excellent sources.
People need small amounts of various vitamins. Some of these, such as vitamin C, are also antioxidants. This means they help protect cells from damage by removing toxic molecules, known as free radicals, from the body.
Vitamins can be:
Water-soluble: The eight B vitamins and vitamin C
Fat-soluble: Vitamins A, D, E, and K
Water soluble vitamins
People need to consume water-soluble vitamins regularly because the body removes them more quickly, and it cannot store them easily.
|Vitamin||Effect of too little||Effect of too much||Sources|
|Unclear, as the body excretes it in the urine.||Fortified cereals and rice, pork, trout, black beans|
|B-2 (riboflavin)||Hormonal problems, skin disorders, swelling in the mouth and throat||Unclear, as the body excretes it in the urine.||Beef liver, breakfast cereal, oats, yogurt, mushrooms, almonds|
|B-3 (niacin)||Pellagra, including skin changes, red tongue, digestive and neurological symptoms||Facial flushing, burning, itching, headaches, rashes, and dizziness||Beef liver, chicken breast, brown rice, fortified cereals, peanuts.|
|B-5 (pantothenic acid)||Numbness and burning in hands and feet, fatigue, stomach pain||Digestive problems at high doses.||Breakfast cereal, beef liver, shiitake mushroom, sunflower seeds|
|B-6 (pyridoxamine, pyridoxal)||Anemia, itchy rash, skin changes, swollen tongue||Nerve damage, loss of muscle control||Chickpeas, beef liver, tuna, chicken breast, fortified cereals, potatoes|
|B-7 (biotin)||Hair loss, rashes around the eyes and other body openings, conjunctivitis||Unclear||Beef liver, egg, salmon, sunflower seeds, sweet potato|
|B-9 (folic acid, folate)||Weakness, fatigue, difficulty focusing, heart palpitations, shortness of breath||May increase cancer risk||Beef liver, spinach, black-eyed peas, fortified cereal, asparagus|
|B-12 (cobalamins)||Anemia, fatigue, constipation, weight loss, neurological changes||No adverse effects reported||Clams, beef liver, fortified yeasts, plant milks, and breakfast cereals, some oily fish.|
|Vitamin C (ascorbic acid)||Scurvy, including fatigue, skin rash, gum inflammation, poor wound healing||Nausea, diarrhea, stomach cramps||Citrus fruits, berries, red and green peppers, kiwi fruit, broccoli, baked potatoes, fortified juices.|
The body absorbs fat-soluble vitamins through the intestines with the help of fats (lipids). The body can store them and does not remove them quickly. People who follow a low-fat diet may not be able to absorb enough of these vitamins. If too many build up, problems can arise.
|Vitamin||Effect of too little||Effect of too much||Sources|
|Vitamin A (retinoids)||Night blindness||Pressure on the brain, nausea, dizziness, skin irritation, joint and bone pain, orange pigmented skin color||Sweet potato, beef liver, spinach, and other dark leafy greens, carrots, winter squash|
|Vitamin D||Poor bone formation and weak bones||Anorexia, weight loss, changes in heart rhythm, damage to cardiovascular system and kidneys||Sunlight exposure plus dietary sources: cod liver oil, oily fish, dairy products, fortified juices|
|Vitamin E||Peripheral neuropathy, retinopathy, reduced immune response||May reduce the ability of blood to clot||Wheatgerm, nuts, seeds, sunflower and safflower oil, spinach|
|Vitamin K||Bleeding and hemorrhaging in severe cases||No adverse effects but it may interact with blood thinners and other drugs||Leafy, green vegetables, soybeans, edamame, okra, natto|
Multivitamins are available for purchase in stores or online, but people should speak to their doctor before taking any supplements, to check that they are suitable for them to use.
Some nutrients also act as antioxidants. These may be vitamins, minerals, proteins, or other types of molecules. They help the body remove toxic substances known as free radicals, or reactive oxygen species. If too many of these substances remain in the body, cell damage and disease can result.
A registered dietitian nutritionist (RD or RDN) studies food, nutrition, and dietetics. To become a registered dietitian, a person needs to attend an accredited university, follow an approved curriculum, complete a rigorous internship, pass a licensure exam, and complete 75 or more continuing education hours every 5 years. Dietitians work in private and public healthcare, education, corporate wellness, research, and the food industry.
A nutritionist learns about nutrition through self-study or formal education, but they do not meet the requirements to use the titles RD or RDN. Nutritionists often work in the food industry and in food science and technology.
Nutrition is the study of food and how it affects the body. People need to consume a varied diet to obtain a wide range of nutrients.
Some people choose to follow a specific diet, in which they focus on certain foods and avoid others. People who do this may need to plan carefully to ensure they obtain all the necessary vitamins to maintain their health.
A diet that is rich in plant-based foods and that limits added animal fats, processed foods, and added sugar and salt is most likely to benefit a person's health.
Find out about different diets here:
- Plant-based diet
- Mediterranean diet
- DASH diet
- Vegan diet
- Raw food diet
- Paleo diet
- Gluten-free diet
- Keto diet
Do you recommend any particular type of diet for overall health?
I firmly believe that there is not a one-size-fits-all diet. Genetics, family history, diagnoses, sustainability, and more factors influence what is the best diet for someone.
However, the basis of any diet that I do recommend for a specific person (whether it is low carb, Mediterranean, Dash, paleo, or keto) is that it is plant-heavy, providing adequate fiber to feed gut bacteria, as well as antioxidants, phytochemicals, and nutrients for optimal health.Natalie Butler, R.D., L.D. Answers represent the opinions of our medical experts. All content is strictly informational and should not be considered medical advice.