It is commonly stated that ‘snack’ foods provide ‘empty calories’ and, therefore elevate energy intake whist providing insignificant quantities of other nutrients. The data presented in the present review suggest that foods which contribute to the pattern of ‘snacking’ contribute significantly to the nutrient quality of the diet. Those who ‘snack’ frequently tend to eat more food in general. Part of the difficulty in identifying the nutritional implications of ‘snacking’ is related to the definitions of ‘meals’ and ‘snacks’ and subsequent categorization of individual patterns. The physiological definitions typically relating to energy content or the time of eating do not necessarily coincide with colloquial, cultural or individual perceptions of what constitutes a ‘meal’ or ‘snack’. Clearly, a more consistent approach would facilitate interpretation of the literature and enable more effective health education messages about ‘snacking’ to be delivered.

The present paper presents a certain number of cultural elements which interact in the determination of the frequency of food intake. Approaches from various perspectives (historical, ethnological, anthropological, sociological) draw attention to two major aspects relating to the periodicity of food intake: the extreme cultural diversity and the continual modifications which have occurred over time and space. The various cultural models change and are subject to multiple influences, for example, cross-cultural, economic and historical. In addition, there are interactions between the models. The definitions of food intake and frequency play a major role in building up consumers' perceptions. These various perceptions are multiple (perception of self, of food and its virtues, the rules and moral values of consumption) and finally influence behaviours. Finally, and taking into account the systems of beliefs, the very nature of feeding behaviours may carry feelings of guilt for the subject. The study of real behaviours and their relationship with health is still incomplete for reasons of methodology and also of conceptual definition. In future, data collection has to take into account real behaviour as well as subjective perceptions and value judgements. A specific effort has to be made in the future to develop methodology. This should allow the collection of reliable data and particularly comparisons between studies, without oversimplifying and distorting cultural specificities.

Although homeostatic mechanisms remain of utmost importance, rhythmic changes are present also. The main ones have a period of 24 h (circadian) or about 2–3 h (ultradian). Circadian rhythms are derived from a body clock, found in the base of the brain, and from the pattern of our sleep wake cycle, including activity and meal times. These rhythms promote the regular changes between an active wake period and a recuperative sleep period. Ultradian rhythms are also widespread and reflect external (lifestyle) and internal factors. The internal factors include biochemical need and some sort of oscillator; but details of how many oscillators, and exactly where they are, remain to be established. Food intake, appetite, digestion and metabolism have been shown to illustrate these principles. Moreover, these principles become important when special circumstances exist as far as meal times are concerned; the particular diffculties of night workers is a good example.

Total energy intake and the frequency and size of meals are profoundly influenced by the socio-cultural context in which it occurs. Simply eating with one other person increases the average amount ingested in meals by 44% and with more people present the average meal size grows even larger. The impact of social facilitation of energy intake on the individual appears to result from genetic effects both on the individuals' sensitivity to the presence of other people and also on the number of other people an individual tends to eat with. Culture markedly affects the choice of foods in the diet and the pattern of meals over the day. However, many of the social, psychological and physical variables that influence intake are similar across cultures.

Several epidemiological studies have observed an inverse relationship between people's habitual frequency of eating and body weight, leading to the suggestion that a ‘nibbling’ meal pattern may help in the avoidance of obesity. A review of all pertinent studies shows that, although many fail to find any significant relationship, the relationship is consistently inverse in those that do observe a relationship. However, this finding is highly vulnerable to the probable confounding effects of post hoc changes in dietary patterns as a consequence of weight gain and to dietary under-reporting which undoubtedly invalidates some of the studies. We conclude that the epidemiological evidence is at best very weak, and almost certainly represents an artefact. A detailed review of the possible mechanistic explanations for a metabolic advantage of nibbling meal patterns failed to reveal significant benefits in respect of energy expenditure. Although some short-term studies suggest that the thermic effect of feeding is higher when an isoenergetic test load is divided into multiple small meals, other studies refute this, and most are neutral. More importantly, studies using whole-body calorimetry and doubly-labelled water to assess total 24h energy expenditure find no difference between nibbling and gorging. Finally, with the exception of a single study, there is no evidence that weight loss on hypoenergetic regimens is altered by meal frequency. We conclude that any effects of meal pattern on the regulation of body weight are likely to be mediated through effects on the food intake side of the energy balance equation.

Dietary and pharmacological approaches to slowing the rate of glucose absorption and blunting the insulin response show promise in the treatment of diabetes and hyperlipidaemia. These approaches include dietary fibre, low-glycaemic-index foods and gastrointestinal digestive enzyme inhibitors. One common feature is that they spread the nutrient load over time. A potentially simpler approach is to take more frequent smaller meals over a longer period of the day. Early studies suggested that frequent glucose and insulin administration to diabetic patients improved diabetes control. More recent acute studies of one test meal or 1 d blood metabolite profiles have identified a significant economy in insulin secretion when glucose is sipped or when meal frequency is increased in both diabetic or non-diabetic subjects. In diabetic subjects improvement in mean blood glucose levels has also been reported. However, despite the demonstration of an alteration in response over time in glucose tolerance in healthy volunteers, no longer-term improvement in glycaemic control was reported in the only study in diabetes to examine a change from three to nine meals daily over a 1- month period. The disparity between longer-term and acute studies requires further investigation. At present, although this nutritional approach holds considerable theoretical promise, specific advice is premature.

Epidemiological data suggesting benefits of increased meal frequency on CHD risk and lipid and lipoprotein levels may be flawed because of biases associated with the method of data collection. In normolipidaemic individuals increasing meal frequency from three to six or more meals daily over a period of several weeks appears to be associated with reduced levels of total and LDL-cholesterol, possibly due to reduced cholesterol synthesis or enhancement of reverse cholesterol transport. However, in non-obese individuals with polygenic hyperlipidaemia and non-insulin-dependent diabetes, altered meal frequency does not appear to confer similar benefits. The reasons for the different responses in these groups of subjects is not clear. The reported effects of altered meal frequency on diurnal levels of triacylglycerols and fatty acids are more variable, with benefits being reported principally in association with meal frequencies exceeding those which might be translated into practical recommendations. Present data preclude recommendations concerning meal frequency on the basis of effects on lipids and lipoproteins. Even in healthy individuals amongst whom benefits have been observed, the periods of observation have been relatively short and it is not known whether adaptation occurs. Further research should focus on longer-term studies in healthy individuals as well as hyperinsulinaemic and diabetic subjects. For those individuals choosing to have a large number of small meals each day, it is relevant to emphasize that no untoward effects of increased meal frequency on lipids or lipoproteins have been demonstrated.

Two areas of sports nutrition in which the periodicity of eating has been studied relate to: (1) the habitually high energy intakes of many athletes, and (2) the optimization of carbohydrate(CHO) availability to enhance performance. The present paper examines how the timing and frequency of food and fluid intake can assist the athlete and physically-active person to improve their exercise performance in these areas. Frequent eating occasions provide a practical strategy allowing athletes to increase energy intake while concomitantly reducing the gastric discomfort of infrequent large meals. The optimization of CHO stores is a special challenge for athletes undertaking prolonged training or competition sessions. This is a cyclical process with post-exercise CHO ingestion promoting muscle and liver glycogen re-synthesis; pre-exercise feedings being practised to optimize substrate availability and feedings during exercise providing a readily-available source of exogenous fuel as endogenous stores become depleted. The timing and frequency of CHO intake at these various stages are crucial determinants for optimizing fuel availability to enhance exercise capacity.

Over the past two decades, substantial research has been conducted to investigate the idea that alterations in short-term nutritional intake play a role in influencing cognitive behaviour and mood. A portion of this research has examined specifically the effect of meal intake on the performance of mental tasks and subjective feelings of mood. Results of this research indicate that a number of variables including the timing and nutritional composition of the meal, nutritional status, habitual patterns of feeding behaviour, beliefs about food, and the nature of the mental tasks, can influence the effects of meals on cognitive behaviour. For example, studies have demonstrated that breakfast intake generally is associated with an improvement in cognitive performance later in the morning, while lunch intake is associated with an impairment in mid-afternoon performance on mental tasks and more negative reports of mood. Intake of nutrients late in the afternoon appears to have a positive effect on subsequent performance on tasks involving sustained attention or memory. Although research has provided insights into the role of meal intake on cognitive behaviour and mood, there are a number of factors which remain to be studied. These include the interaction of age, gender, activity level, meal composition, personality factors, stress with the effects of meals on cognitive behaviour. Additionally, more work is needed on the time-course of short-term nutrient effects, and the effects of chronic changes in meal intake on behaviour.

In the last 20 years, mainly due to optimum fluoride exposure, and practice of good oral hygiene procedures, an important reduction in caries has been observed, despite the fact that sugar consumption was maintained and/or was increasing during the same lapse of time. A sugar-caries relationship cannot be established in most of the industrialized countries and the dietary factor is not as preponderant in the caries process as it used to be two decades ago. The factors which seem to contribute the most significantly to the cariogenicity of the diet are the frequency of carbohydrate ingestion and eating patterns. The relative cariogenicity of food is not correlated with the amount of carbohydrate it contains. Even if sucrose remains the most important sugar consumed in sweets, beverages and confectionery products, all fermentable-carbohydrate foods can be involved in the caries process. The use of chewing gum and other xylitol-containing products have resulted in defined reduction in caries and represent interesting alternatives for high-caries-risk populations. Caries risk and oral health assessments as well as the evaluation of oral hygiene procedures and fluoride exposure should become essential tools in dietary counselling. People who receive optimum fluoride exposure and follow regular oral hygiene measures can safely use dietary carbohydrates, preferably during meals and two to three times daily in snacks or drinks.