If we are to make reasoned judgements on the interrelationship of beer and human health, then it is important that we rst consider the key elements of nutrition.
Essentially our bodies require, in the correct balance, the key nutrients for healthy functioning and development. Additionally the diet should be devoid of materials that are damaging. In this context there may be components of our daily intake that, while not of themselves essential nutrients, may serve to counter negative impacts of adverse food constituents or materials present in the environment. For more detailed considerations of human nutrition the reader is referred to Boyle and Zyla (1996).
Our bodies need food to provide energy (calories) and the building blocks of our tissues (notably amino acids), for the most part taken into the body in the form of protein, carbohydrates, lipids, vitamins, minerals and water. Our wellbeing is therefore incon-trovertibly related to what we eat and drink, in terms of the content of the essentials, the form in which they are present in the food (e.g. carbohydrate in the form of bre acts bene cially in a way quite distinct from that carbohydrate that will overtly provide energy through digestion) and the presence or absence of molecules in the food that may be bene cial or damaging to the body.
If any individual component of the diet is present in excess or is insuf cient in quantity, then the diet is out of balance.
Energy
The main sources of energy for the human body are carbohydrates, fats and proteins. However, especially in the context of this book, we must stress that alcohol is a source of energy.
Energy in food is quanti ed on the basis of calories, one calorie being de ned as the amount of heat required to raise the temperature of one gram of water by one degree Celsius. It is customary to talk in terms of kilocalories (or Calories with a capital C) which equate to 1000 calories. These days it is more scienti cally correct to talk in terms of kilojoules, for the joule has replaced the calorie as the primary unit of energy under the international system of units (SI). (Incidentally, James Prescott Joule, 1818-89, after whom the unit of energy was named, was a member of a famous Staffordshire brew-
ing family.) One joule is de ned as the amount of energy exerted when a force of one newton is applied over a displacement of one metre. It is the equivalent to one watt of power radiated or dissipated for one second. However, calorie is so widely known and used as a term that I employ it here: the term calorie is proving impossible to shake from popular parlance. The reader should be warned that often calorie (without the capital C) is employed in the literature rather than kilocalorie.
The number of calories in a foodstuff can be determined in the laboratory by combustion. However the 'true' calori c content of a food as it pertains to the diet depends on the extent to which those calories are available to the body.
This applies to all components of the diet. Just because something is present in high quantity in a foodstuff it does not necessarily follow that it will get into the body to exert any effect. Many factors may impact, including the form in which the nutrient is present in a food. A metal such as iron may not be assimilated if it is attached to some other component of the diet that passes straight through the gut. Much of the modern work on antioxidants is awed in this way. For example, only if the speci c antioxidants get into the body will they get to the key site where they are able to act.
Returning to carbohydrates, those such as starch and sugar are almost completely digested and oxidised by the body and they are ascribed a calori c value of 3.75 kcal/g. Fats, which are digested up to 95%, afford a higher energy level (9 kcal/g) because they are less oxidised than the carbohydrates. The calori c value of protein is generally held to be similar to that of carbohydrate, at 4 kcal/g. Ethanol is ascribed a calori c value of 7 kcal/g, indicating that, molecule for molecule, it is an extremely rich source of energy, second only to fat.
If calories in excess of those needed to maintain the body in equilibrium are taken in, then the surplus will be built up in the form of fat, for the simple reason that, pound for pound, fat is a richer energy store than is starch or protein. The converse applies: enhanced energy demand through exercise will 'burn up' fat provided that the extra calorie requirement is not met from fresh food intake.
Phytonutrients
The importance of antioxidants is highlighted in the California pyramid, with the baseline here occupied by foodstuffs, notably fruits and vegetables, which are rich in these and other 'phytonutrients' (i.e. plant-derived nutrients). People living on plant-rich diets generally appear to have lower incidence of disease. This has prompted a search for the active ingredients, of which some are undoubtedly antioxidants. Others may regulate enzyme action and in uence the production or elimination of relevant components. Thus there has developed a large market for herbal supplements. It is in this context that attention has been paid to the hop (see Chapter 6).
Phytochemicals are de ned by the US Food Administration as substances of plant origin that may be ingested by humans daily in gram quantities and which exhibit the potential for modulating metabolism such as to be favourable for cancer prevention and cardiovascular protection (Rincon-Leon 2003). The word 'nutraceutical' has crept into common parlance.
For those preferring their phytonutrients in food - as opposed to supplement - form, Gollman and Pierce (1998) offer one useful recipe book. The authors endeavour to present their recipes from an underpinning scienti c perspective. Alas, beer is not featured. Wine is - yet we will discover in Chapter 6 that beer is likely at least the equal of wine from a health perspective.
Carbohydrate, fat and protein
Although carbohydrate, fat and protein are interchangeable through pathways of intermediary metabolism in the body, the relative amounts of each are not irrelevant. Carbohydrates, then, can 'spare' protein if they are present in adequate quantities. If they are not, then the body will use protein, which is a key component of muscles and other body tissues. Health experts suggest that about 60% of calorie intake should be as carbohydrate. Even within a category, there can be signi cant differences. More complex forms of carbohydrate, e.g. starch, will linger in the body longer than will simpler sugars, allowing the growth of microbes to take place and the attendant enrichment of vitamins in the uxing food. The converse can apply. Some individuals are lactose-intolerant, with this sugar being poorly absorbed and leading to attendant diarrhoea.
For proteins, a key feature of their value in the diet is their relative content of the various amino acids. The best proteins are those containing all of the essential amino acids (which the human body cannot synthesise) presupposing that those proteins are indeed taken up by the body. Meat, sh, milk and egg proteins are generally good. Barley protein is relatively de cient in two amino acids, lysine and (to a lesser extent) threonine, though high lysine variants have been developed (Kasha et al. 1993).
Of course most diets don't usually contain just a solitary source of protein, and generally there is an appropriate mix of animal and vegetable proteins.
The fats provide the essential fatty acid, linoleic acid, which the human body cannot synthesise. Unsaturated fatty acids of this type are associated with a lower incidence of coronary heart disease: they lower cholesterol levels. Beer is essentially fat free.
Vitamins are organic substances that the human body cannot synthesise itself and which must be provided in the diet (Finglas 2003). They have various functions in the body and are customarily divided into the water-soluble vitamins and the fat-soluble vitamins; they are summarised in Table 4.2. For the most part they are not required in very large quantities, but it must be borne in mind that the composition of the food matrix in which they are present can impact on their availability. One example is the higher requirement for thiamine if alcohol is present at high levels. It is equally important to stress that excessive intake of vitamins may have adverse effects. For the most part this pertains to two of the fat-soluble vitamins, A and D, though B6 at levels above 50 mg per day or nicotinic acid in excess of 2-6 g per day are of concern for neurological damage and liver damage respectively
Fibre
The term is unfortunate, for not all of the components generally considered under this heading are actually brous. Perhaps 'roughage' after all is no worse a term (Kritchevsky
& Bon eld 1995).
The majority of materials considered to be dietary bre are plant cell wall components including celluloses, hemicelluloses (such as are found in the cell walls of barley) and pectins. There can be a further division into soluble and insoluble fractions, though it must be remembered that this refers to what is solubilised in standard laboratory analytical procedures and not necessarily what happens in the gastrointestinal tract.
Insoluble components may serve to delay the digestion of other components via physical blocking. The soluble components, on the other hand, will afford increased viscosity if they are of high molecular weight, thereby lengthening transit time in the gut and also the rate at which digestion products (e.g. glucose) are taken through the gut wall. This may also explain the impact of dietary bre in reducing the absorption of cholesterol.
These materials hold water, lead to a softening of stools and accelerate the passage of the stool through the large intestine. Research in recent years has demonstrated the merits of bre in lowering plasma cholesterol levels, reducing cancer incidence, lessening the need for diabetics to take insulin, and so on. The understanding of the precise structural features in bre which lead to best effect is less than clear (see Johnson 2003). The beer carbohydrates comprising soluble bre (which will include the degradation products of barley cell wall polysaccharides and also the dextrins produced during starch degradation; see Chapter 3) escape absorption in the small intestine, thus becoming nutrients for bacteria located in the large bowel. The importance of these organisms to gut function and health has become well recognised in recent years and has led to the concept of probiotics and prebiotics. Probiotics are organisms, notably lactobacilli and bi dobacteria, which are added to diet to boost the ora in the large intestine. For example they are added to yoghurt (Young 1998). Prebiotics are nutrients that boost the growth of these organisms. These may include oligosaccharides that may promote the growth of the appropriate organisms (Gibson 1999; Roberfroid 2001). Microbes in the large intestine produce methane and other gases as a result of their metabolism, and the atulence experienced after drinking beer may relate to this activity .
It also needs to be borne in mind that materials capable of binding to the bre passing straight through the digestive system will also be less available to the body. This might include certain minerals and vitamins (Prosky 2003).
Water
The human body is almost two-thirds water. Loss of 5-10% of the body weight as water leads to symptoms of dehydration. Evidently the greater the risk of water loss, the greater the need for rehydration. Clearly if the water is also carrying away with it other nutrients, e.g. minerals, then these will need to be replaced in quantities that restore the status quo.
Balance
To reiterate: the diet needs to be in balance. And this includes 'trendy' food ingredients - the so-called functional food ingredients. Excessive bre can lead to problems with intestinal gas, perhaps intestinal obstruction, and a reduced absorption of essential minerals such as zinc, iron and calcium. Uptake of minerals can also be restricted by chelating agents such as phytate and oxalate. Polyphenolics can bind metals such as iron and so reduce uptake. Phosphates reduce the uptake of zinc while calcium interferes with assimilation of manganese. Another example is that high levels of antioxidants such as vitamin C can switch over and become pro-oxidants.
As is said more than once in this book, beer should be taken in moderation as part of a balanced diet. The same goes for all other foodstuffs.
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