Fresh vegetables are important components of a healthy diet. A healthy diet is one that helps maintain or improve health. It is important for the prevention of many chronic health risks such as: obesity, heart disease, diabetes, and cancer.[1] A healthy diet involves consuming appropriate amounts of all nutrients, and an adequate amount of water. Nutrients can be obtained from many different foods, so there are a wide variety of diets that may be considered healthy diets. Overview Macronutrients Protein Protein is needed primarily for repair and growth of the human body. Protein consists of amino acids, some of which can be made from other proteins, some of which are essential amino acids. A healthy diet requires sufficient quantities of all essential amino acids. Increased requirements of amino acids occur for repair of muscles after strength training and a small amount is used for growth. Amino acid requirements are largely dependent on muscle mass; men generally require larger dietary protein intake for this reason. Some strictly epidemiological evidence shows an increased mortality with high red meat intake.[2] Fat Main article: Fat Fat is used in the body for forming cell membranes, oxidised for energy, and can be stored by the body for later use if food intake is inadequate. Fats come in three main types: saturated fat, monounsaturated fat and polyunsaturated fat. Trans fat, a kind of unsaturated fat found in large quantities in foods such as margarine, is now known to be harmful. Carbohydrate Carbohydrates are chemicals that can be broken down in the body to simple sugars like glucose, fructose. Glucose is primarily used by the body in muscles but is the primary energy source used by the brain. If an excess of carbohydrate is consumed then it is stored with a large quantity of water as glycogen in the skeletal muscles and the liver. Fructose cannot be used by the skeletal muscles, but is converted into glucose by the liver. However if large quantities of fructose are consumed, the conversion produces triglycerides which are thought not to be healthy. One major source of fructose is sucrose (table sugar), fruits also contain substantial quantities, and so should not be taken in excess. Energy The human body creates energy from chemical reactions (mainly oxidation) of food. Due to conservation of energy if more energy is absorbed from food, then weight gain occurs (in the form of glycogen and its associated water) and fat. Some variation in weight can also occur due to hydration levels. Different components of the diet provide different number of net calories, roughly speaking proteins provide about 4.5 kCal, carbohydrates about 5 kCal and fats, 9.5 kCal per gram. Research has showed that the idea of thin people having a 'fast metabolism' is false; human beings burn energy at quite predictable rates, and gain or loss of weight is mostly to do with calorie intake versus the bodies' basal metabolism (with people with more lean bodyweight burning more calories) as well as (usually to a lesser degree) activity levels; with any long-term excess being stored as fat. Energy is also used for growth and repair. Minerals Salt While a moderate amount of salt is required for health, a high salt diet can have detrimental effects on blood pressure[3]: Potassium Potassium is used by the body for a number of purposes, and tends to lower blood pressure. An inadequate supply can cause heart arrhythmias. Magnesium Main article: Magnesium in biology#Food sources Magnesium salts are used in the nervous system, and tends to lower blood pressure. They are mostly water soluble and so are easily absorbed. Calcium Calcium is used by the body to form and maintain bones and teeth and is used in the nervous system. Inadequate supply can result in osteoporosis. Iron Iron is used by the body to form red blood cells, which carry the oxygen for the body. Lack of iron can cause anemia. High doses of iron in a short period cause death. Copper Although toxic in high doses, copper is an essential nutrient. Low levels cause progressive failure of the nervous system. Up to around half of the copper can be obtained from drinking water fed by copper pipes. Zinc Zinc is an essential component of many thousands of chemical processes throughout the body. A deficiency can cause skin problems, but also impairs the immune system and can cause impairment of repair and growth. Chromium Chromium is used by the body to process carbohydrates. High doses of chromium are toxic. Selenium Main article: Selenium Although selenium is an essential trace mineral it is toxic at high doses. At normal levels it is used by the body to produce antioxidant chemicals, and some studies show an inverse relationship between intake and cancer, and the studies seem to show that it is unwise to be deficient in it. Few foods are high in selenium; one exception is Brazil nuts; one and half brazil nuts per day give the recommended intake. Vitamins Main article: Reference Daily Intake The target amount of vitamins that are thought to be needed for good health are expressed as RDA (Recommended Daily Allowance) or Reference Daily Intake (RDI). RDAs vary somewhat with age, sex and bodyweight and may be increased or reduced by medical conditions. Fiber Main article: Dietary Fiber Fiber in the diet may be of benefit to health. There is some evidence that fiber lowers LDL cholesterol but does not lower HDL cholesterol.[4][5] Healthy diets There are a number of diets and recommendations by numerous medical and governmental institutions that are designed to promote certain aspects of health. World Health Organization The World Health Organization (WHO) makes the following 5 recommendations with respect to both populations and individuals:[6] * Achieve an energy balance and a healthy weight * Limit energy intake from total fats and shift fat consumption away from saturated fats to unsaturated fats and towards the elimination of trans-fatty acids * Increase consumption of fruits and vegetables, legumes, whole grains and nuts * Limit the intake of simple sugars * Limit salt / sodium consumption from all sources and ensure that salt is iodized Other recommendations include: * Sufficient essential amino acids ("complete protein") to provide cellular replenishment and transport proteins. All essential amino acids are present in animals. A select few plants (such as soy and hemp) give all the essential acids. A combination of other plants may also provide all essential amino acids. Fruits such as avocado and pumpkin seeds also have all the essential amino acids.[7][8] * Essential micronutrients such as vitamins and certain minerals. * Avoiding directly poisonous (e.g. heavy metals) and carcinogenic (e.g. benzene) substances; * Avoiding foods contaminated by human pathogens (e.g. E. coli, tapeworm eggs).