To combat thinning hair in women, you should start from the inside out. A proper and well balanced diet is the beginning of a successful program to have healthy hair.
Of course, as in any diet, it is essential to eat in a well balanced way with a variety of foods from all of the food groups. I like to think of it as eating by color and texture. By adding different foods with all of the colors and textures, you can increase your chances of giving yourself all of the needed nutrients. Not only will you improve your hair, but your entire body will reap health benefits. Fortunately, this is not a diet that you have to suffer through, either. Imagine how much nicer a simple green salad of stir fry will be if you add bright red peppers, fresh yellow summer squash, sweet red onions, and slices of vivid orange carrots.
Diets with more seeds, nuts, and whole grains can provide added nutrients that boost hair growth. Appropriate and healthful oils like canola oil, olive oil, fish oil, and flax seed oil can also prevent thinning hair.
For women thinning hair or hair loss can be a sign of a problem in the gastrointestinal tract. It could be a sign of insufficient stomach acids; It could also mean a deficiency of protein, zinc and other nutrients. Taking two acidophilus tablets after or between meals (four to six tablets per day) for two months will help.

For men balding process can be slowed down by taking a low-fat diet. Some scientists postulate that the male pattern baldness is tied to increased testosterone levels during puberty. A high-fat, meat-based diet raises testosterone levels, and that may adversely affect hair follicles. For example, in Japan, male pattern baldness was very rare prior to World War II when the diet was lean and healthy. The Japanese now consume a more fatty, Westernized diet. Baldness is now increasing substantially among Japanese men. Eating low-fat foods may not stop hair loss; but it might help slow down the hair loss.
Anemia is one of the most frequent causes of hair loss. Eat plenty of iron-rich foods, like liver (Avoid if you are pregnant) and other organ meat, whole grain cereals, dark green leafy vegetables, eggs, dates, and raisins.
The hair is comprised mostly of protein. To encourage hair growth, adhere to a diet rich in protein. A recommended diet for this purpose includes calves liver, brewer's yeast, wheat germ, and two tablespoons of granulated lecithin. Along with protein, these foods are also high in B vitamins, an important nutrient for hair.