Good nutrition along with vitamins and minerals are essential for survival. Nutrients are chemical substances supplied from the environment and food that are essential for survival of organisms. The two types of nutrients that are essential for survival and good health are macronutrients and micronutrients. Macronutrients are needed in large amounts such as can be found in proteins, fats, and carbohydrates. Micronutrients are essential in small doses and include vitamins and minerals, therefore, they need to be taken in through food and supplements. For example, carbohydrates including sugars and starches serve as the primary energy sources for cells. Proteins such as meats are important for body processes including tissue repair, antibody formation, muscle maintenance, and digestive enzyme production. The body will show signs of poor nutrition through the hair. An indicator of low iron in the diet is dry brittle hair that tangles when wet and can be hard to comb through. Hair loss can result if iron levels are too low in the body causing a condition known as anemia. Digestive problems can cause many issues in the body such as malabsorption of nutrients which can lead to hair loss. Celiac disease is a digestive system disease that damages the small intestine and inhibits the body's ability to absorb nutrients from food. When the body cannot absorb nutrients, the body will not function properly. The hair receives last whatever is absorbed in the body; therefore, if the body is blocking nutrients, hair loss will occur. When organisms become undernourished, and other body parts begin to malfunction, the hair becomes brittle, loss of lusture and falls out.