Human nutrition can be looked at from two directions: what you need
to get out of your food, and what foods you should eat to get those
nutrients.
Calories. This is the "fuel" that keeps your body running. The unit is kilocalories per day, where 1 kcal = 4180 joules. Recommended amounts:
Carbohydrate. This should be your main source of calories. Carbohydrates are starch (e.g. bread, rice, oatmeal, potato) and sugar (e.g. fruit, junk food). It all has the same fuel value, but you digest starch much better than large quantities of sweets, which tend to overload your liver.
Fat. Animals prefer fat because of its high fuel value, 9 Kcal/gram. However, humans get much too much fat. Getting over 30% of your calories from fat is very unhealthy; 20% is a good target; 10% is necessary for people trying to mitigate active heart disease. Saturated (solid) fat is hardest on your blood system; avoid at all costs. Liquid fat (cooking oil) is better, but also tends to get rancid inside your body; use the minimum feasible amount. Soybean and canola (rapeseed) oil are cheap and good. Cottonseed oil may have pesticide residues. Keep in a closed bottle away from heat.
Beef has the most saturated fat. Pork has less. Chicken has less than pork. Remove visible fat from meat when cooking or when eating. More expensive cuts of meat have fat globs throughout; don't buy it. Egg yolk has a lot of (nonsaturated) fat; egg white has none. The fat content of milk is marked on the carton; 1% "low fat" milk is a good compromise between flavor and fat content. ("Reduced fat" means 2%. Standard is 3.2%.)
Protein. Your body needs protein to replace worn-out cellular components. The recommended amount for an adult is 0.8 g/Kg.day, or 56 g/day for a standard 70 Kg male. (It's 2.0 g/Kg.day for an infant.) Chicken is 23% protein by mass, and other meat is generally similar; thus the 70 Kg male needs 240 g/day (1/2 lb) if that's his only protein source, which it isn't. (It's generally believed that the standard recommendation is higher than needed.)
Your body needs about 21 amino acids to make protein, but some can
be transformed into others. "Essential" amino acids are those which
the body cannot make. Animal protein (meat, milk, eggs, not including
gelatin) has all the essential amino acids in the proportions found
in the animal. Plant protein generally lacks various essential amino
acids. However, mixtures of plants can provide complete protein.
In particular, beans plus alkali-treated corn (
Vitamins. These are chemicals involved (mostly) in energy production, which your body cannot make for itself. They are needed in small quantities. Antioxidant vitamins (indicated by a * in the table) protect you from damage due to reactive oxygen species which are byproducts of energy metabolism.
Units in the table below are per day. "IU" means international unit. The "RDA" is the official recommended daily allowance, which is set somewhat above the level that is known to cause deficiency diseases. The last column gives a recommendation that in some cases reflects what we actually get, and in some cases is considerably higher but is recommended by a certain nutrition writer.
With vitamins it is not true that more is better
.
Particularly, 5000 IU/day should be taken as an upper bound for vitamin
A; more is bad for your immune system. 400 IU/day is an upper bound
for vitamin D except under medical supervision; with an excess, calcium
is lost from the bones.
| Ltr | Name | RDA | Recom. |
|---|---|---|---|
| A | Carotene | 5000 IU | 5000 IU |
| C * | Ascorbic acid | 60 mg | 500 mg |
| D | Calciferol | 400 IU | 400 IU |
| E * | Tocopherol | 30 IU | 400 IU |
| B1 | Thiamine | 1.5 mg | 10 mg |
| B2 | Riboflavin | 1.7 mg | 10 mg |
| B3 | Niacin | 20 mg | 100 mg |
| B6 | Pyridoxin | 2 mg | 10 mg |
| B12 | Cyanocobalamin | 6 mcg | 6 mcg |
| Folic acid | 400 mcg | 500 mcg | |
| Biotin | 300 mcg | 500 mcg | |
| Pantothenic acid | 10 mg | 50 mg |