VOL: 97, ISSUE: 32, PAGE NO: 52
Shupikai Rinomhota, MSc, RGN, RMN, PGCE, RNutr, is nursing lecturer, University of Leeds
Hazel Rollins, MSc, RGN, RM, is nutrition nurse specialist, Luton and Dunstable NHS TrustMembers of the informed public are familiar with the word metabolism. However, the word means different things to different people - those being cared for and those engaged in the caring process. We need to consider metabolism and the factors associated with it in relation to one of the greatest challenges in health care delivery - obesity.
Members of the informed public are familiar with the word metabolism. However, the word means different things to different people - those being cared for and those engaged in the caring process. We need to consider metabolism and the factors associated with it in relation to one of the greatest challenges in health care delivery - obesity.
The Weight of the Nation: Obesity in the UK (Jebb, 2000) yields some gloomy statistics: 17% of men and 20% of women are currently obese and over half the adult population is overweight. It also warns that, were current trends to continue, more than 25% of the UK adult population will be obese by the year 2010.
Worldwide statistics show that, in 1997, 45% of men and 36% of women had a body mass index (BMI) of 25-30, indicating that they were overweight, while 11% of males and 14% of females had a BMI of 30-40, showing that they were obese (World Health Organization, 1998).
Health care professionals are faced with two challenges - the first is to ensure that patients are adequately nourished with palatable and nutritious food when ill or in hospital, and the second to ensure that the issues of obesity and being overweight are addressed and the message on the implications of obesity to the health of the individual continues to be one of the main priorities of health care delivery.
Aspects of energy balance
Metabolism refers to the sum process by which materials are broken down and built up in the various organs, tissues and cells of the body. It controls all the chemical reactions in the body in order to keep it working properly.
The breaking-down process is known as catabolism, and during this process energy is released. The building-up process is known as anabolism, and during this process energy is used up. Following digestion or the breakdown of food in the digestive system, the food substances that are absorbed are involved in catabolic and anabolic processes. The basal metabolic rate (BMR) is the amount of energy an individual expends when completely rested and lying down and awake after fasting for 12 hours.
BMR is affected by gender, age and weight and is predictable. It can be calculated using simple equations: the heavier a person is, the higher the BMR; the more muscle one has, the higher the BMR and the older one gets, the slower the BMR. Thus, metabolism, catabolism and anabolism are important in as far as understanding what happens to food components at cellular level.
However, it is necessary to understand that for weight gain to occur energy intake must exceed energy expenditure. Some people might like to ascribe their weight gain to altered metabolism, even though this is not the case. Indeed, Prentice et al (1986) showed that there were high levels of energy expenditure in obese women caused by their larger body size, thus disputing the wrongly held misconception that individuals become obese because their metabolism has slowed down.
While congenital metabolic defects that may lead to obesity exist, these are the exception rather than the norm. For most people weight gain is a result of the imbalance between what goes in and what is spent. In a healthy individual total energy expenditure is influenced by the three things mentioned that affect BMR (gender, age and weight) and by physical activity. Other factors that influence total energy expenditure at other times are tissue growth, tissue repair, pregnancy, lactation and dietary thermogenesis (increased production of heat after eating).
The foods that individuals prefer to eat are determined by individual taste, upbringing and culture. It does appear that energy-dense foods are highly preferred across all geographical, ethnic and cultural boundaries (Nestle et al, 1998). Of course, in today's world acculturation continues to occur and this can be a good thing, especially in breaking bad food habits. Acculturation refers to the process by which groups and individuals adopt the norms and values of an alien culture (Fieldhouse, 1995).
However, Nestle et al (1998) expressed concern that some individuals enter a nutrition transition whereby acculturation leads to negative nutritional effects, such as the preference of a diet higher in fat.
It does appear that children have a preference for high-fat foods (Birch, 1992) which may be related to parental adiposity (Fisher and Birch, 1995), and this preference no doubt is likely to continue into adult life (Drewnowski et al, 1992). The latter authors seem to dispute the fact that carbohydrate preference is a characteristic feature of human obesity, arguing that their study showed that carbohydrate-rich foods were listed as preferences only if their fat content was also high or if the foods were sweet.
More recently, Oliver et al (2000) found that stressed emotional eaters ate more sweet high-fat foods, such as cakes, chocolate and biscuits, and more energy-dense meals than unstressed non-emotional eaters did.
Mood and comfort eating
Studies by Lieberman et al (1986), in which obese individuals were allowed to choose their meals and snacks from high-carbohydrate and high-protein foods with the same amount of calories, showed that the sample under study could be divided into carbohydrate cravers and non-carbohydrate cravers. They argued that the behaviour in which some individuals show increased frequency of snacking on carbohydrate-dense foods may be reinforced by mood after consumption of such foods. They observed that carbohydrate cravers consumed 700-800kcal in snacks in addition to the 2000kcal consumed in meals and reported positive mood (feeling less depressed) on three self-report mood questionnaires.
Other studies and reviews (de Castro, 1987; Keith et al, 1991; Ottley, 2000) have supported this finding, even though the mechanism is still unclear and the interaction between what is eaten and mood state is believed to be very subtle.
It is well accepted that appetite is increased during the winter months due to increased metabolic needs. Indeed, Schutz and Garrow (2000) showed seasonal fluctuations in body weight, with a higher body weight in winter than spring and summer. The explanation for this is that the amount and type of diet consumed is different with each season, with more energy dense foods being consumed in winter. However, the association between depression or seasonal affective disorders and an increased appetite for carbohydrate-rich foods (Wurtman and Wurtman, 1989) still needs to be explored further.
There appears to be carbohydrate craving in depression (Hopkinson and Bland, 1982), in premenstrual syndrome (Wurtman and Wurtman, 1989), during the luteal phase (Barr et al, 1995) and in obesity (Lieberman et al, 1986). In some individuals, craving for certain foods is associated with binge eating. There is a hypothesis that binge eating may change the way the body responds to leptin, a key appetite-suppressing hormone that is produced by fat tissue (Knight, 1999). Leptin levels in blood rise and suppress appetite until more energy is needed. In some individuals this mechanism fails to work, resulting in individuals possibly becoming insensitive to their leptin.
Nutrients that boost mood
Can an individual eat a particular food and feel better? The simple answer is yes and no. This is because, in practice, most foods people eat contain all three macronutrients of carbohydrates, protein and fats, albeit in various proportions, as well as the micronutrients of minerals and vitamins. This makes it difficult to narrow down which food component is being most effective as far as mood is concerned. Indeed, while Reid and Hammersley (1999) highlight methodological issues in previous studies on mood and carbohydrates, they accept that studies by Spring et al (1989) to some extent support this relationship.
Psychologically individuals feel better after eating foods that they like and enjoy or those that have a special meaning for them. Some people do eat more for comfort, whatever their food preference, when feeling low in mood and/or when experiencing stressors. This type of eating contributes to the weight gain and obesity that are reaching epidemic proportions.