Just how much of an influence does diet have in somebody's health? According to Fred Pescatore, MD, author of The Hamptons Diet, diet has the biggest influence on someone's health except for accidental injury, as diet plays a role in six of the top ten leading causes of death in the US. Here's a look to the link between some common health problems and poor dietary habits.

PROBLEM: Weakness, fatigue

Possible cause: Fatigue is most affected by one's level of hydration, says Keller. "Unfortunately, by the time you sense you are thirsty, you're already partially dehydrated." A diet low in carbohydrates also contributes to fatigue, as the body uses carbohydrate as its preferred energy source.

Cure: Keller recommends awell-rounded diet that relies heavily on frequent consumption of nutrient-rich foods, with plenty of water all day long. "Moisture-rich fruits and vegetables can help with weakness and fatigue as well, as they provide not only water, but fiber, and vitamins and minerals that help replenish us."

When to see a doctor: If changing your diet and getting adequate rest don't improve the symptoms, as this could indicate other problems, such as mononucleosis or depression. "Don't delay - the body should respond favorably within 30 days."

PROBLEM: Hair Loss

Possible cause: Hair loss occurs in different people at different times in their lives, and a good part of it is genetic. "Hormones also play an important role in maintaining hair thickness," adds Keller. A diet too low in calories or lacking in protein, iron or certain vitamins can also affect the health of your hair.

Cure: Keller recommends plenty of vitamin C and A-rich foods, along with foods rich in omega 3 fatty acids, such as salmon, oranges and red bell peppers. Also, make sure you're eating enough calories for your body type (a minimum of 1200 for women and 1500 for men).

When to see a doctor: If the condition worsens or if your hair falls out in clumps, which could indicate a thyroid condition.

PROBLEM: Headaches

Possible cause: Pescatore emphasizes the importance of finding out which foods you are sensitive to so you can make dietary changes. Caffeine and sugar withdrawal are also common causes. "Nitrates found in preserved foods and nitrites in wines can give people headaches as well."

Cure: Start by avoiding the offending foods.Certain supplements, such as feverfew, have been proved to help. "High doses of vitamins B6 and magnesium for a week should cure the headaches."

When to see a doctor: Headaches can indicate a serious problem, and should be checked by a doctor if they don't improve within a few days or if the pain is so strong that it interferes with everyday activities.

PROBLEM: Mood swings, short-term depression

Possible cause: Mood swings are most often associated with hormonal changes and high protein diets, which can make you edgy and irritable.

Cure: Keller recommends eating 5 mini-meals per day, with at least 10 glasses of water. "There is also some interesting research in the area of vitamin B6 and its role in alleviating depression."

When to see a doctor: "Again, I wouldn't let it go for longer than a month. The body tends to respond quickly to a healthy regimen."