7 classes of food and their functions

Food is defined as any substance consumed to provide nutritional support for an organism. Food is usually of plant or animal origin, and contains essential nutrients, such as carbohydrates, fats, proteins, vitamins, or minerals. The substance is ingested by an organism and assimilated by the organism’s cells to provide energy, maintain life, or stimulate growth. Historically, humans secured food through two methods: hunting and gathering and agriculture, which gave modern humans a mainly omnivorous diet. Worldwide, humanity has created numerous cuisines and culinary arts, including a wide array of ingredients, herbs, spices, techniques, and dishes.

Food may contain colours (natural and synthetic), flavours, pharmacologically active substances (such as caffeine, steroids, and salicylates, which chemically affect the body), natural toxicants (naturally occurring poisons, such as cyanide), additives and various contaminants (substances resulting from a contaminated environment, such as pesticides). Even characteristic flavours such as those of oranges and passionfruit can depend on the presence of a dozen or more chemicals.

In Addition, the chemical nature of food is changed by storage, preservation and, especially, by cooking. Food chemicals can also interact amongst themselves within the body. For example, the availability to the body of iron from plant sources depends on the amount of vitamin C present in the food eaten. The way in which carbohydrate is absorbed from the bowel depends to some extent on the presence of dietary fibre, even though the fibre itself is not absorbed.

The 7 Classes Of Food and Their Functions


Carbohydrates are found in a wide array of both healthy and unhealthy foods—bread, beans, milk, popcorn, potatoes, cookies, spaghetti, soft drinks, corn, and cherry pie. They also come in a variety of forms. The most common and abundant forms are sugars, fibers, and starches. Foods high in carbohydrates are an important part of a healthy diet. Carbohydrates provide the body with glucose, which is converted to energy used to support bodily functions and physical activity. But carbohydrate quality is important; some types of carbohydrate-rich foods are better than others:

The healthiest sources of carbohydrates: unprocessed or minimally processed whole grains, vegetables, fruits and beans—promote good health by delivering vitamins, minerals, fiber, and a host of important phytonutrients.

Unhealthier sources of carbohydrates include white bread, pastries, sodas, and other highly processed or refined foods.  These items contain easily digested carbohydrates that may contribute to weight gain, interfere with weight loss, and promote diabetes and heart disease.

The Healthy Eating Plate recommends filling most of your plate with healthy carbohydrates – with vegetables (except potatoes) and fruits taking up about half of your plate, and whole grains filling up about one fourth of your plate. Examples: Maize, Yam, Potatoes, Garri, Rice and Millet. READ: Nigerian Foods and Beverages to Avoid During Pregnancy



Proteins are super important for all animals including humans. Our bodies use proteins to create our muscles, send messages, and even grow hair. Protein food is dense with energy, and it’s thought that one of the reasons humans have such big brains and are so clever is we began eating cooked meat. All the energy from that meat gave us the extra resources to grow big brains and complex nervous systems. Because of this energy, a diet rich in protein is super important for children, pregnant and lactating women, and those recovering from an injury.

There are also 10 essential proteins that humans need to live and cannot create themselves. That means the only way for us to get these necessary proteins is to consume them in our diet. Examples of protein food include beans, meat, dairy, eggs, whole grains, soy products, and legumes.



Fiber is actually a type of carbohydrate. Fiber mostly comes from cellulose, a long, complex carb that people (unlike cows and other herbivores) cannot digest. That’s okay though, because we don’t eat fiber for energy. Instead, fiber helps to keep everything in the digestive tract moving along properly. A diet high in fiber reduces your chance for colon cancer and helps to keep bowel movements regular. It slows down the digestion of other foods, preventing insulin spikes. A good rule of thumb for snacks is more than 2 grams of fiber for every 10 grams of sugar. Of course, the more fiber and the less sugar the better! Whole grains, fruits, and vegetables are all good sources for fiber. Fiber comes in two varieties, both beneficial to health:

Soluble fiber: which dissolves in water, can help lower glucose levels as well as help lower blood cholesterol. Foods with soluble fiber include oatmeal, nuts, beans, lentils, apples and blueberries.

Insoluble fiber: which does not dissolve in water, can help food move through your digestive system, promoting regularity and helping prevent constipation. Foods with insoluble fibers include wheat, whole wheat bread, whole grain couscous, brown rice, legumes, carrots, cucumbers and tomatoes. The best sources of fiber are whole grains, fresh fruits and vegetables, legumes, and nuts.


Fat and Oil

Approximately no more than 35% of our daily calories should come from fat. Fats are a great source of energy: 1g of fat provides 9 calories. Fat protects the internal organs, however, too much fat can be damaging. Fat is also a great insulator and fat stored just below the skin acts to insulate the body from the cold. Females require a minimum level of body fat in order to maintain menstrual function as fat cells secrete and are the store for oestrogen. It is advised to limit the number of saturated fats and oil consumed as they are strongly correlated with an increased amount of cholesterol in the blood, which in turn increases the risk of heart disease and diabetes. Saturated fats can be found in beef, lamb, pork, butter, cream, milk, cheeses, coconut oil, palm oil and cocoa butter. It’s important to replace saturated fat with unsaturated fat. This means eating more fish, avocados, nuts and seeds and plant-based oils and spreads such as flax seed oil and soya spread.



Vitamins are complex organic substances found in our food which support almost every system in the body, including the immune system, the brain and the nervous system. Many of them help convert food into energy and help the body to use carbohydrate, fat and protein. They are also involved in regulating growth, making red blood cells and protecting the body from harmful free radicals. Only very small amounts of vitamins and minerals are needed to enable the body to work properly and prevent illness. Vitamins K and D cannot be manufactured by the body and must come from our food.

To get more vitamins into your diet, try and eat foods as fresh and unprocessed as possible. Choose fruit and vegetables that have been produced locally rather than those that have had to travel across the world. Try cooking vegetables as light as possible, keeping their crunchy texture. Avoid slow cookers and lengthy cooking techniques. Microwaving, steaming or pressure-cooking vegetables is the kindest to vitamins.



Minerals are elemental substances and are found in the soil. They are absorbed by plants, which we eat or are eaten by animals – which we then eat. Therefore we can get minerals from both animal and vegetable sources. Minerals have many different roles, including structural roles, such as calcium in bones and teeth or regulator roles such as sodium and potassium in fluid balance and muscle contractions. Minerals do not deteriorate in the same way that vitamins do because they are ‘elemental’ they cannot be easily destroyed by heat, light or air.



Water is one of the most important macronutrients along with carbohydrates, proteins and fats. We can live a little longer without food (around 8 weeks) than we can water (only a few days). A 12% drop in body weight through water is always fatal. Our body is made up of around 65% water, it assists with absorption, digestion, excretion and aids circulation of nutrients around our body. Water is also essential for regulating our bodies temperature and distributing heat. Water also lubricates our bodies moving joints and our eyes.

How much water should we be drinking?

Individual requirements of fluid intake vary considerably. This is due to various factors which depend on the amount of fluid being lost, for example environmental temperature, humidity, individual metabolism, activity levels and the individual’s health and diet. On average a Man (70 kg) should be drinking 2.5 liters a day, a Women (58 kg) should be drinking 2.2 liters of water a day and for children (10 kg Child) 1 liter and a Child (5 kg) should be drinking 0.75 liters a day. Many foods that we eat particularly fruit and vegetables contain high amounts of water. On average most healthy adults should drink at least 6 to 8 glasses of liquid every day.

How does water leave the body?

Water is mainly lost from the body by urine, breathing and sweating, we lose around 1.5 liters a day. Dehydration can occur when fluids are not replaced. If we lose even just 1-2%, it can result in dehydration symptoms such as thirst and dry mouth will start to appear. In addition, 3-4% vague discomfort and loss of appetite appears, difficulty concentrating, headache and sleepiness are observed at 5%. Tingling and numbness of extremities can occur at 6% and collapse at 7% dehydration. A 10% loss of water through dehydration is life-threatening. Therefore it is very important that we maintain our hydration levels correctly throughout the day.

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