Chapter 3: Food and Diet

What is this post going to be about?

Take a guess. Take a wiiiiiiild guess.

...

It's going to be about... FOOD AND DIET!!

(Sorry, no prizes for getting that one right.)

The most important topic to cover here is nutrients, or all the helpful stuff that you get in food that help your body cells to function normally. Some also provide energy for the cells. Today I'm going to write about a wide variety of nutrients, namely sugars, amino acids, fatty acids, vitamins, minerals and water.

First up are simple sugars. Remember those carbohydrates that I talked about yesterday? Yup, I'm talking about them. We get these sugars from the carbs in our diet, mainly in the form of sugar, starch and cellulose. Carbohydrates are the main energy source for the cells. They first get broken down into simple sugars (remember, starch and cellulose are polysaccharides, which are long chains of molecules made up of monosaccharides, or simple sugars), which are then broken down further to release energy. Excess carbohydrates are stored as glycogen in the liver and muscles, but if there's way too much then the remaining carbs get converted into fat, which is stored all around the body.

Aside from obvious sources of sugar, like lollies and other things that should be eaten in moderation (hehe... "should"), sugar can also be found in fruit. Starch, a long-chain carbohydrate, is found in cereals, wheat, rice, oat, corn, bread and certain vegetables such as potatoes, peas and dried beans. Cellulose is found in foods of plant origin, particularly unrefined foods, since it is the material that plant cell walls and fibres are comprised of. Cellulose, however, cannot be digested by humans and therefore cannot provide energy for cells or matter for building new ones, though cellulose can stimulate the contraction of the muscular walls of the intestine. Cellulose, and foods like it, can therefore be called insoluble fibre or roughage (since it can't be digested but it promotes movement of food in the intestines).

Next up are amino acids, which I also talked about yesterday as they're the building blocks of proteins. Unsurprisingly, we get amino acids from proteins. The body breaks down proteins into amino acids and then uses the amino acids to build required proteins- kinda like breaking apart a Lego house and then using the pieces to build a dinosaur. Proteins, as explained yesterday, are part of the structural material of the cell. Some are enzymes in cellular reactions. Excess proteins can be converted to carbohydrates in order to be used as energy or stored as fats. By the way, protein and carbohydrates provide the same amount of energy per gram: roughly 17kJ/g.

There are 20 different amino acids, some of which can be produced in the body. There are, however, nine amino acids which cannot be produced in the body. These are known as essential amino acids. Proteins containing sufficient quantities of these amino acids are known as "complete proteins" or "first-class proteins." These can be found mostly in animal-based foods. Plant-based foods tend to have "incomplete proteins" or "second-class proteins," but if a wide variety of foods are eaten you will still be able to obtain all of the essential amino acids.

Fatty acids have a pretty bad rep at times but they are necessary too. They are, however, only necessary in small quantities. Fatty acids allow cells to make certain fats which are necessary for body functioning. Also, foods containing fatty acids also contain fat-soluble vitamins, like vitamins A, D, E and K. Fatty acids are probably best known for being stored as a reserve of energy- and they contain a lot of energy! When utilised, they contain 37kJ of energy per gram- more than double the energy yield of carbohydrates or proteins!

You've probably already had a list of foods containing fatty acids drilled into your head from various sources, but here's a quick list: butter, margarine, milk, cheese, oils etc.

Next up is vitamins. There are several different kinds of vitamins, and they all come from different sources and have different functions within the body. You can get all of the vitamins that you need from a varied, balanced diet, but they cannot be manufactured in the body. Vitamins do not provide energy, but they're essential for regulating cellular reactions and for cells to gain energy from proteins, carbohydrates and fatty acids.

Minerals are taken into the cells as ions from mineral salts. These include phosphates and sodium chloride (a.k.a. salt). Just like vitamins, a balanced diet should provide you with adequate amounts of minerals, except for a few notable exceptions, like calcium, iron, iodine, zinc and fluorine. In order to balance this, water supplies in several countries are fluoridated (bringing a lot of protest from some people, especially conspiracy theorists), and table salt is often iodised.

Just like vitamins, different minerals have different functions within the body. Secretory cells in the stomach require chloride ions to produce hydrochloric acid (HCl), cells in the bone marrow that produce red blood cells require iron to produce haemoglobin and bone cells require magnesium and calcium. Of course, there are many other processes that require minerals- these are just some examples.

Water! The essence of life! You need plenty of water to live- an average person loses around 3L a day, and you obviously lose more if you're in a warm climate or doing lots of exercise- but you don't need to guzzle lots of it, as most solid food is half water. A small amount of water is also produced in chemical processes in cells. (That's not to say that you don't need to drink water. You do, since the water in food and produced in chemical processes is not adequate.)

So why is water so important? It's an important solvent in the body- many chemicals are dissolved in it. It also regulates body temperature, and is important in the excretion of bodily wastes. If you don't have enough water, you can become constipated and/or get kidney stones, and if you are really really dehydrated, you can even get kidney and heart failure. So drink yo' water, kids!

Now that I've gone through all of the main essential nutrients, it's time to talk a bit more about energy, that stuff produced by carbohydrates, proteins and fatty acids. We all know that we need energy to go about our daily activities, but what else does the human body need energy for?

Answer: the human body also needs energy to grow and repair tissues, to maintain body temperature and to maintain normal body functions. You wouldn't want your heart to go without energy!

The process by which carbohydrates, lipids and proteins are broken down to provide energy is called respiration. The energy comes from the bonds between the atoms in the molecules. If more energy is consumed than required, the excess is stored as fat, as you probably know already.

How much energy do you need? That's not a super straightforward question, as it depends on a lot of factors:

1. Basal metabolic rate, or BMR (i.e. how much energy you need when you're resting. Obviously you're still using some energy when you're resting, as your heart needs to beat and you need to breathe.)
2. Amount of physical activity.
3. Body size: more body mass = more energy required to move around
4. Gender: women generally require less energy since they have a higher proportion of body fat, which weighs less than muscle (see point 3 about how more mass = more energy required)
5. Age: you need more during periods of rapid growth (such as adolescence), but older people generally require less due to decreased metabolic rate and often decreased physical activity.
6. Climate: you need more energy in colder climates to maintain body temperature.
7. Pregnant women need more energy for the developing foetus. Lactating women (lactation = milk production) also need more energy to produce all of that milk.

Aside from each individual having different energy requirements, certain groups also have different requirements for particular nutrients. For example, pregnant women need to consume more folic acid, calcium, iron and protein and lactating women need more calcium. Vegans might need to take some supplements, as certain vitamins might be lacking in their diet, particularly B12, which is only found in foods of animal origin. (Normal vegetarians are normally fine but they do need to be careful to maintain a balanced diet.)

Some foods nowadays also have particular beneficial ingredients added to them. For example, some flour now contains vitamin B1 (thiamine). Some yoghurts contain probiotics, margarines might have extra calcium or fish oil, or drinks might have some extra fibre included. These are known as functional foods.