Considerable debate has taken place regarding issues surrounding protein intake requirements.How much protein needed in a person's daily diet is determined in large part by overall energy intake, as well as by the body's need for nitrogen and essential amino acids. Physical activity and exertion as well as enhanced muscular mass increase the need for protein. Requirements are also greater during childhood for growth and development, during pregnancy or when breast-feeding in order to nourish a baby, or when the body needs to recover from malnutrition or trauma or after an operation.It was suggested, that protein intake amount should be measured by using three parameters (which should be viewed together): absolute intake (g/d), intake per body weight (g/body kg) and intake as energy percent.
If enough energy is not taken in through diet, as in the process of starvation, the body will use protein from the muscle mass to meet its energy needs, leading to muscle wasting over time. If the individual does not consume adequate protein in nutrition, then muscle will also waste as more vital cellular processes e.g. respiration enzymes, blood cells) recycle muscle protein for their own requirements.
According to US/Canadian Dietary Reference Intake guidelines, women aged 19–70 need to consume 46 grams of protein per day, while men aged 19–70 need to consume 56 grams of protein per day to avoid a deficiency.U.S recommended daily protein dietary allowance, measured as intake per body weight, is 0.8 g/kg.However, this recommendation is based on structural requirements, but disregards use of protein for energy metabolism.Several studies have concluded that active people and athletes may require elevated protein intake (compared to 0.8 g/kg).Suggested amounts vary between 1.6 g/kg and 1.8 g/kg, while a proposed maximum daily protein intake would be approximately of 25% of energy requirements at approximately 2 to 2.5 g/kg.However, many questions still remain to be resolved.