Food Groups…

Apologies – this has ended up being a long read. Don’t feel you have to do it all in one. I will post separate pieces on much of this in the future. This might be a useful page to refer back to in the future.

Graphics like this annoy me slightly. The information is good but I don’t like the how the foods are grouped. Words like dairy & vegetable are too unclear and not scientific enough for my liking. I break dietary components down into seven key groups. They are…

Water, Protein, Fat, Carbohydrate, Fibre, Vitamins and Minerals

Water

Humans contain a lot of water. All the chemical reactions that occur within your body happen dissolved in water so it is important to remain well hydrated. Be guided by your thirst – if you are thirsty have a drink. You could get all the water you need to survive from the food you eat but water in milk, cups of tea, fizzy drinks, soup etc contributes to your total water consumption. However, drinks that contain lots of added sugar may have other effects so drinking plain water, a little and often, is the best option. If you drink too little water your urine will be dark – this is a clue that you may need to drink more during the day.

Protein

Protein in your diet comes from meat, fish, cheese, eggs, beans and nuts. Between 20% and 30% of your dietary energy should come from protein. You need about 0.8 g of protein for every gram of body mass so if you have a mass of 50 kg you should be eating about 40 g of protein each day. In the UK we eat rather more protein than is recommended, which is OK as long as the source of protein is healthy. Red meat, cheese and processed foods often contain other things like saturated fat (see below) that you should try to limit in your diet. Protein from fish, nuts and beans does not have this disadvantage so you can tuck into them!

Protein is broken down into amino acids in your body. These are the building blocks that your cells require to make all the enzymes and other proteins your body needs to function. Each gene is the code to make a single protein and it is important that you supply your body with the raw materials to make sure that your genes can express themselves properly.

Fat

Fat (or lipid) is a necessary component of your diet. It provides energy, can be stored for insulation and converted into other useful compounds. Some vitamins (see below) are fat soluble so you need fat for them to work properly. Fat has about twice the energy per gram as starch so too much can lead to unwanted weight gain. No more than 25% of your energy should come from fat. Bile produced by the gall bladder helps the fat to mix with water in your digestive system. Then an enzyme called lipase breaks it down into smaller molecules called fatty acids. Because fat and water do not mix, it takes longer to digest fat than other components of your diet. There are two main types of fat…

Saturated fat is fat where the chain of carbon atoms are joined to each other by single bonds. This sort of fat is found in dairy products like butter and cream, and in beef and lamb. It is generally considered less healthy than other forms of fat.

Unsaturated fat (polyunsaturated fat) is fat that has some double bonds between the chains of carbon atoms. These act as points where digestive enzymes can attack and they are easier to break down and turn into other products. Fish oil, olive oil and sunflower oil are good sources of unsaturated fats.

Carbohydrate

Carbohydrates consist of sugar, starch and fibre – but I will list fibre separately because it is indigestible. Carbohydrate should be the main source of energy in your diet, making up about 50% of your energy intake. Carbohydrates are compounds of carbon, hydrogen and oxygen.

Sugars (like glucose and fructose) are very quickly absorbed into the bloodstream. Glucose is very biologically active, which means that it has an immediate effect upon your metabolism. Your body has to deal with this glucose immediately. It will either use it for respiration or store it away as fat – it can’t just float around in your blood! The hormone insulin is responsible for controlling your blood glucose level. Starch and fat (and other sugars) are broken down into glucose by your digestive system.

Starch is a complex chain of glucose molecules all linked together. The enzyme amylase can break it back down into sugars. Starch is found in seeds – rice, wheat, maize – and starchy tubers like potatoes. Anything made from flour will have a high starch content.

Fibre

Strictly speaking fibre (dietary fibre or roughage) is also a complex hydrocarbon like starch. However, this time the glucose molecules are joined in a more intricate fashion to make the macromolecule cellulose which is indigestible by humans. Animals that can digest cellulose (cows, monkeys etc) usually rely on populations of micro-organisms living in their gut to do the actual digesting. Fibre gives your food bulk so that the intestinal muscles have something to work against and it helps to keep your food moving through your system. The medical consensus seems to be that we need about 30 g of fibre each day. Apparently most of us only consume about 20 g. Three bowls of All-Bran (a high fibre cereal) would give you about 36 g of fibre. An apple (roughly 200 g) has about 4.5 g of fibre so seven apples will just about hit your target. 750 g (¾ kg!) of Brussel sprouts ought to do it too. Eating a variety of things is a much more sensible option!

Vitamins

Vitamins are organic molecules that your body cannot synthesise (make for itself) so needs to get from the food you eat. Typically they are needed in tiny quantities – only mg per day. There are 13 vitamins – A, C, D, E & K (fat soluble) plus the eight B vitamins (water soluble). I think you can get by knowing about…

Vitamin A, from carrots, milk, eggs & oily fish. It prevents a condition known as night blindness which makes it harder for you to see in low light levels.

Vitamin C, in fruit, sprouts and broccoli, prevents scurvy and also helps wounds to heal quickly.

Vitamin D – the sunshine vitamin – present in oily fish and eggs. It helps to promote healthy teeth and bones. The government is currently suggesting that people take it as a supplement in the winter months. You can synthesise Vitamin D when sunlight shines directly on to your skin.

Minerals

These are elements (usually metals) that you need in tiny amounts in your diet. Again, just milligrams per day. The ones you should know about are…

Iron, needed for healthy blood and to prevent anaemia, present in red meat, beans, nuts and breakfast cereals.

Calcium, needed for healthy teeth and bones, present in dairy products and leafy greens.

Iodine – a non-metal one for good measure. Present in milk, eggs, sea fish and shellfish. It is needed to help your thyroid make hormones such as thyroxine, which regulate your metabolism.

That is a lot of reading. Sorry. Don’t feel you have to deal with it on one day. Come back for revision!

Questions…

1. Which food group should provide most of your energy?
2. Which food group is needed for the growth and repair of your tissues?
3. What is another word for lipid?
4. Suggest a good food to supply Vitamin A.
5. Suggest a good source of iron.
6. A lack of iron results in anaemia, which is when your body cannot make haemoglobin. What symptoms might you observe in someone who does not have enough haemoglobin?
7. Broccoli is 2.6% fibre by mass. How much would you have to eat to fulfil your recommended daily allowance of fibre?