A person's caloric requirement depends on his body size and exercise level. Sedentary people of both genders will keep their weight stable by taking in about 13 calories per pound of body weight each day. Moderate physical activity boosts this requirement to 16 calories a pound, and vigorous exercise calls for about 18 calories a pound. On average, a moderately active 125-pound woman needs 2,000 calories a day; a 175-pound guy with a similar exercise pattern needs 2,800 calories. And like women, men will lose weight only if they burn more calories than they take in.
Young adults. Teen girls and young women usually need more calories than when they were younger, to support their growing and developing bodies. After about age 25, a woman’s resting metabolism (the number of calories her body needs to sustain itself at rest) goes down. To maintain a healthy weight after age 25, women need to gradually reduce their calories and increase their physical activity.
There's not much doubt about this one: Women need more iron than men, because they lose iron with each menstrual period. After menopause, of course, the gap closes. The RDA of iron for premenopausal women is 18 mg a day, for men 8 mg. Men should avoid excess iron. In the presence of an abnormal gene, it can lead to harmful deposits in various organs (hemochromatosis). Since red meat is the richest dietary source of iron, it's just as well that men don't need to wolf down lots of saturated fat to get a lot of iron.
Try not to think of certain foods as “off-limits.” When you ban certain foods, it’s natural to want those foods more, and then feel like a failure if you give in to temptation. Start by reducing portion sizes of unhealthy foods and not eating them as often. As you reduce your intake of unhealthy foods, you may find yourself craving them less or thinking of them as only occasional indulgences.
"These products provide a subtle, incremental effect. You can't use a sports supplement for a week and expect to gain pounds of muscle, but if used properly, research shows they can provide a slight, not overwhelming, edge," says Andrew Shoa, PhD, vice president for regulatory affairs for the Council for Responsible Nutrition, a trade association for the dietary supplement industry.
Now, the benefits of good nutrition are fairly obvious to most of us. You have more energy, your health improves, and your productivity blossoms. Healthy eating also plays a huge role in maintaining a healthy weight, which means a decreased risk of type 2 diabetes, certain cancers, heart problems, high blood pressure, and a host of other health ailments. (Genetics also plays a significant role. I'm not some crazy person who thinks genes don't matter.)
Recent research shows that differences in the content of the selenium in the soil can cause major differences in the concentration of selenium in meat.  For instance, since the soil in Finland is poor in selenium, the authorities decided in the early 1980s to add selenate to commercial fertilizers. A survey of selenium status among 108 healthy young people showed an increase in the blood selenium level of about 50 percent after four years. 
Low-fat dairy products are excellent sources of calcium. Other good sources of calcium include salmon, tofu (soybean curd), certain vegetables (broccoli), legumes (peas and beans), calcium-enriched grain products, lime-processed tortillas, seeds and nuts. If you do not regularly consume adequate food sources of calcium, a calcium supplement can be considered to reach the recommended amount. The current recommendations for women for calcium are for a minimum of 1,200 mg per day.
In addition to diet, exercise and other lifestyle factors can also play an important role in bone health. Smoking and drinking too much alcohol can increase your chances of developing osteoporosis, while weight-bearing exercise (such as walking, dancing, yoga, or lifting weights) can lower your risk. Strength or resistance training—using machines, free weights, elastic bands, or your own body weight—can be especially effective in helping to prevent loss of bone mass as you age.