There has been much research and many theories into the link between diet and disease.

Any of the following, may indicate poor nutrition in a human.

-Obese people often experience breathing difficulties.

-Backache may occur as a result of obesity.

-Too much food, particularly fat and carbohydrates, will lead to obesity. Too little food will cause wasting of the tissues and ultimately starvation. Failure to thrive in children may be a sign of marasmus (too little energy intake) or kwashiorkor (too little protein and energy intake).

-Heart disease can occur as a result of obesity, and heart failure may be a result of extreme anorexia nervosa as the balance of electrolytes is disturbed.

-Softening of the bones may be a sign of rickets (lack of vitamin D).

-Loss of motor function in the legs may be a sign of beriberi (lack of vitamin B1, or thiamine).

-Lesions in the spinal cord may be a sign of vitamin B12 deficiency.

-There are a number of conditions affecting the stomach and digestive system as a result of diet.

-Symptoms may include diarrhoea, nausea, vomiting, pain and cramps.

-Stones may form in the kidneys as a result of insufficient fluid; obese people may be prone to kidney failure.

-Adrenal glands may enlarge as a result of pantothenic salt deficiency (related to the B vitamins).

-The formation of gallstones is associated with a fatty diet.

-Too much alcohol may cause cirrhosis of the liver.

-Insufficient iron will cause anaemia.

-Constipation can be caused by lack of fibre in the diet.

-Piles (haemorrhoids) may also be a result of lack of fibre.

-Swelling and painful feet may be a sign of vitamin B12 deficiency.

-Numbness in the toes may be a sign of vitamin deficiency.

-The hair may become dull and brittle, or it may fall out or change colour.

-Headaches may be related to vitamin deficiency.

-Night blindness may arise from lack of vitamin A.

-The tongue may become inflamed as a result of a number of vitamin deficiencies.

-Bleeding gums may be a sign of scurvy (vitamin C deficiency).

-Enlargement of the thyroid gland (goitre) may be linked to iodine deficiency.

-Rashes, itching, soreness, scaliness and cracking of the skin may be a sign of a number of vitamin deficiencies.