Human Nutrition – Phytonutrients, Carbohydrate, fat and protein

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 influence 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.

Phytochemicals are defined 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 favorable 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 endeavor to present their recipes from an underpinning scientific perspective. Alas, beer is not featured. Wine is – yet  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 significant 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 food. The converse can apply. Some individuals are lactose-intolerant, with this sugar being poorly absorbed and leading to attendant diarrhea.

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 synthesize) presupposing that those proteins are indeed taken up by the body. Meat, sh, milk and egg proteins are generally good. Barley protein is relatively deficient 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 synthesize. 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

Vitamins are organic substances that the human body cannot synthesize 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 summarized in Table below. 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 (Finglas 2003).

Minerals

The table lists the requirements of the human for minerals and their various impacts. Minerals comprise only 4–6% of the body (Freeland-Graves & Trotter 2003) and some of them are needed only in vanishing quantities. Calcium, chloride, magnesium, phosphorus, potassium and sodium are the major minerals. Chromium, copper, fluoride, iodide, iron, manganese, silicon and zinc are needed in trace quantities. Arsenic, boron, molybdenum, nickel, selenium and vanadium are ‘ultra trace’ minerals.

Fibre

The term is unfortunate, for not all of the components generally considered under this heading are actually fibrous. Perhaps ‘roughage’ after all is no worse a term (Kritchevsky & Bon eld 1995).

The majority of materials considered to be dietary fibre 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 fibre 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 fibre which lead to best effect is less than clear (see Johnson 2003). The beer carbohydrates comprising soluble fibre (which will include the degradation products of barley cell wall polysaccharides and also the dextrins produced during starch degradation;  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 recognized 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 flora in the large intestine. For example they are added to yogurt (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 flatulence experienced after drinking beer may relate to this activity.

It also needs to be borne in mind that materials capable of binding to the  fibre 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 fibre 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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