A higher dietary intake or serum concentration of betaine has been associated with greater lean body mass in middle-aged and older adults. However, it remains unknown whether betaine intake is associated with age-related loss of skeletal muscle mass (SMM). We assessed the association between dietary betaine intake and relative changes in SMM after 3 years in middle-aged adults. A total of 1242 participants aged 41–60 years from the Guangzhou Nutrition and Health Study 2011–2013 and 2014–2017 with body composition measurements by dual-energy X-ray absorptiometry were included. A face-to-face questionnaire was used to collect general baseline information. After adjustment for potential confounders, multiple linear regression found that energy-adjusted dietary betaine intake was significantly and positively associated with relative changes (i.e. percentage loss or increase) in SMM of legs, limbs and appendicular skeletal mass index (ASMI) over 3 years of follow-up (β 0·322 (se 0·157), 0·309 (se 0·142) and 0·303 (se 0·145), respectively; P < 0·05). The ANCOVA models revealed that participants in the highest betaine tertile had significantly less loss in SMM of limbs and ASMI and more increase in SMM of legs over 3 years of follow-up, compared with those in the bottom betaine tertile (all Ptrend < 0·05). In conclusion, our findings suggest that elevated higher dietary betaine intake may be associated with less loss of SMM of legs, limbs and ASMI in middle-aged adults.

An investigation was carried out to determine whether there were significant changes in nutrient intake over 17 years of adult life. The Medical Research Council National Survey of Health and Development is a longitudinal study of a nationally representative cohort of singleton births in the UK in 1946. Of this cohort, 1253 survey members provided information on diet recorded in a 5 d diary at age 36 years in 1982, 43 years in 1989 and 53 years in 1999. The outcome measures were mean intakes of energy, macronutrients, minerals and vitamins. There were significant changes in the intake of most nutrients in 1999 compared with previous years. Intakes of fat, Na, Fe and Cu have fallen, but there was a rising trend in the intakes of Ca, P, carotene, thiamin, pyridoxine, folic acid and vitamins C, D and E in both men and women. Additionally, intakes of K, Mg and vitamin K1 have risen in women. There were significant gender differences, women showing a higher percentage rise in the intakes of carotene, riboflavin, folic acid, vitamin C and vitamin E. These changes were related to changes in the consumption of certain key foods, such as the increased consumption of fruit and vegetables and a shift away from whole milk, butter and red meat. Most of these trends are in line with accepted nutritional guidelines. How far these changes are due to consumer choice and real changes in food composition or are due to artefacts inherent in the methodology is discussed.