Summary by Philip James, Stig Sjolin and Philip White

Adolescence is a time of emotional, physical and educational transition when the ado- lescent’s medical and nutritional needs have to be seen in the context of children seeking to es- tablish their identity in a changing adult world. Their selfawareness and search for an adult identity often leads to a lability of mood and a fluctuating attitude to society’s conventions of behaviour including food patterns.

The nutritional needs of the adolescent popu- lation vary enormously because the sequence of physcial changes begins at different times in dif- ferent individuals. Thus some teenage boys may normally persist with their childhood physique for several years after other boys of equivalent chronological age have attained sexual develop- ment and an adult stature and physique. On the average girls have their growth spurt before boys and are, for about 2 years, taller, heavier and more muscular. These biological differen- ces have important effects on behavioural atti- tudes and on nutritional needs. The onset of the adolescent growth spurt varies among popula- tions and is strongly influenced by the popula- tion’s nutritional state.

In several affluent countries the secular shift towards a greater adult height and towards ear- lier maturation appears to have halted. The progression towards earlier maturation and greater adult heights is not immutable. Histori- cal analyses show a reversal in the secular shift when there is an acute increase in the cost of staple foods e.g. bread. Within a society one often finds differences in the timing of pubes- cence between social classes. This may relate to nutritional factors but the identity of the re- sponsible nutrients remains uncertain. In the populations of industrialized countries, how- ever, about 90 To of the variation in the onset of the growth spurt seems to be determined by genetic factors.

The variability in the timing of the growth spurt and in the tempo of growth means that calculations to the supposed average nutritional needs of the adolescent are inappropriate for many if not most children. Estimates of nutri- tional requirements are based on inadequate in- formation. The accumulation of body nutrients with growth suggests marked increases in nutri- ents requirements which may not always be met. Calcium requirements are high during the growth spurt but the body’s capacity to adjust calcium absorption to needs may explain the ab- sence of evidence of calcium deficiency. Iron re- quirements are also increased, particularly in girls after the onset of menstruation; the inci- dence of iron deficiency is appreciable and ex- acerbated by pregnancy.

The patterns of eating vary widely among adolescents and this is a time of maximum en- ergy intakes. Snacks i.e. any dietary item eaten between meals, are consumed by nearly all children and need not necessarily signify nutri- tionally inappropriate eating. Nevertheless the increase in alcohol consumption is of great con- cern, particularly in view of its association with road traffic accidents, often the leading cause of death in adolescents. The risk of alcohol de- pendance being established in adolescence is great.

Despite the eccentricity of eating patterns of many adolescents their food intakes are surpris- ingly satisfactory from a nutritional standpoint. The consumption of such beverages as soft drinks mimicks the adult utilization of alcoholic drinks with an equivalent low nutrient density. With the problem of alcoholism in adults it is not surprising that some teenagers during their transition in behavioural pattern beging to drink alcoholic beverages too much. Similarly many adolescents avoid breakfast and engage in dietary practices designed to reduce their

NUTRITION REVIEWSIVOL. 39, NO. 2IFEBRUARY 1981 115

weight. About half of the adolescent girls in western societies attempt weight Teduction in order to change their body image. Obesity occurs in 5-15 Vo of adolescent girls and inappropriate slimming practicies are rife. Sev- ere energy restriction is often counterpro- ductive, leading to a variety of symptoms which are found in children with overt anorexia ner- vosa. Obesity developing in adolescents tends to persist but detailed councelling and support in the best programmes can help about half the . children to attain a persistently normal weight. Advice to exclude all snacks tends to isolate teenagers from the hormal social life of their peers and may be counterproductive. Rigid sys- tems for dieting may accentuate the social press- ures to slim and increase the risk of anorexia nervosa. Some cases of anorexia nervosa are primarily a nutritional rather than a psychiatric problem.

Many adolescents modify their diets to cope with the almost universal problem of acne even though the scientific evidence relating dietary practices to the prevalence of acne is absent. The development of acne is probably multifac- torial but does depend on androgen secretion. Epidemiological evidence on the prevalence of acne is scanty and the recognized beneficial ef- fects of exposing the skin to sunlight compli- cates an analysis of other environmental factors such as diet. Assessing treatment programmes for acne is also very difficult and most test: of

dietary regimens have led to conflicting results. Excessive intake of iodide may, however, exacer- bate the condition. There is also suggestive evi- dence to warrant further work on the role of zinc, essential fatty acids and vitamin A in modifying the severity of acne.

One of the most important nutritional impli- cations of the adolescent’s shift to adult pat- terns of behaviour is that feeding habits change and evidence suggests that eating patterns stabil- ize after the adolescent phase and persist into adult life. Adolescence is therefore a time of opportunity for health and nutrition education but this must be offered in the context of the adolescent’s style of life. The progressive reduc- tion in physical activity of most adolescents in an affluent society favours the development of obesity. A reduction in food intake to ac- commodate to the fall in physical activity is not an appropriate response. Physical activity re- quires generous additional food and thereby in- creases the probability of obtaining all needed nutrients. Thus the priority in nutrition educa- tion should be to encourage the adolescent to remain physically active as a necessary part of a programme aimed at improving health.

As developing countries become more afflu- ent, care should be taken to ensure that there is not an appreciable decline in physical activity of adolescents because otherwise the nutrition problems of the affluent world may be superim- posed on those already present.

116 NUTRITION REVIEWSIVOL. 39, NO. PlFEBRUARY 1981