Weight Is Key to Protein Requirements

Study Shows Protein in Diet {diet [ˈdaiət]n.日常饮食；(病人的)特种饮食 vi.节食} Should Be Based on Weight, Not Age

Nov. 7, 2008 -- The amount of protein an adult needs to stay healthy is based on weight, not age.

That's according to a new study published in the American Journal of Clinical{clinical ['klinikəl]a. 临床的} Nutrition{nutrition [nju:ˈtriʃən]n.营养}.

As people age, their metabolism{metabolism [məˈtæbəlizəm]n.新陈代谢}and physiology{physiology [ˌfizi'ɔlədʒi]n. 生理学} usually change. And these changes can influence{influence [ˈinfluəns]n.影响(力)；势力，权势 vt.影响} a person's nutritional{nutritional [nju: 'triʃənəl] a. 营养的,滋养的} needs. Although many researchers believe that older adults require more protein than younger adults, it's not reflected in the current Recommended{recommend [ˌrekəˈmend]vt.推荐；劝告；使受欢迎} Dietary{dietary ['daiətəri] a. 饭食的,饮食的n. 规定的食物,饮食的规定} Allowance{allowance [əˈlauəns]n.津贴，补贴，零用钱} (RDA) and Estimated{estimate [ˈestimət, ˈestimeit]n.估计，估量；评价，看法 vt.估计，估量} Average Requirement (EAR), which are the same for all healthy men and women aged 19 and older.

The RDA and EAR for protein is 0.80 grams and 0.66 grams of protein per kilogram{kilogram [ˈkiləgræm]n.千克，公斤} of body weight per day, respectively{respectively [riˈspektivli]ad.各自地，各个地，分别地}. That's an RDA of about 54 grams of protein a day for a 150-pound adult, or approximately{approximately [əˈprɔksimətli]ad.近似地，几乎正确地} 1.5 chicken breasts{breast [brest]n.胸脯，乳房} and a 7-ounce steak{steak [steik]n.牛排，肉排，鱼排}.

Wayne Campbell, PhD{PhD n. 哲学博士} a researcher and professor of foods and nutrition at Purdue University, and colleagues{colleague [ˈkɔli:g]n.同事，同僚} developed a study to test whether protein requirements actually change with age.

The researchers recruited 42 people to participate{participate [pɑ:ˈtisipeit]vi.(in)参与，参加} in the study: 11 young men, 12 young women, eight older men, and 11 older women. The age range for the younger and older adults was 21 to 46 and 63 to 81.

Each participant{participant [pɑ:ˈtisipənt]n.参加者，参与者} underwent{undergo [ˌʌndəˈgəu]vt.经历，遭受} three 18-day study periods{period [ˈpiəriəd]n.(一段)时间，时期；课时；句号} in which his or her diet was firmly{firmly [ˈfə:mli]ad.坚固地，稳定地} restricted{restrict [riˈstrikt]vt.限制，约束，限定}. During each 18-day trial, they were given 63%, 94%, or 125% of the Recommended Dietary Allowance of protein. They were also allowed to eat their usual diet for at least one week between the study periods.

During the 14th to 17th day of each trial, the researchers measured the participants' nitrogen{nitrogen [ˈnaitrədʒən]n.氮} balance. Nitrogen balance determines{determine [diˈtə:min]vt.确定；决定；使下决心 vi.下决心} the difference between how much nitrogen (mainly from protein) a person is ingesting{ingest [inˈdʒest]v.咽下，吞下} and excreting (as waste). Healthy adults eliminate{eliminate [iˈlimineit]vt.排除，消除，根除；淘汰} the same amount of nitrogen as they consume{consume [kənˈsju:m]vt.消耗；吃完，喝光；(with)使着迷；烧毁}.

Researchers say the study shows that younger and older adults don't require different amount of protein to be healthy. This means that the RDA of 0.8 grams of protein per kilogram of body weight should be adequate{adequate[ˈædikwit]a.充足的,足够的；适当的,胜任的} for virtually every older person.

However, in an editorial{editorial [ˌediˈtɔ:riəl]a.编者的；社论的 n.(报刊的)社论，重要评论} accompanying the study, Joe Millward, PhD, the head of nutrition and safety at the at the University of Surrey, England, writes that even though the study shows that an adult's daily protein requirement is likely to be independent{independent [ˌindiˈpendənt]a.独立的，自主的；中立的；无关的} of age, it should not "be classed as definitive{definitive [diˈfinitiv]a.最可靠的，权威性的；决定性的} in terms of the absolute magnitude{magnitude [ˈmægnitju:d]n.重要性，重大；巨大，广大} of the requirement." He notes the difficulty in precisely{precisely [priˈsaisli]ad.精确地；刻板地} assessing nitrogen balance.