"Eat to Live, Not Live to Eat"
John H Weisburger, 2000
To minimise the onset of chronic diseases in aging populations, health authorities worldwide recommend we eat more fruit and vegetables and less animal-based foods. Plant-based diets are low in calories and saturated fats with good supplies of carbohydrate, fibre, vitamins and minerals. They also have no cholesterol and most importantly are rich sources of bio-active phytochemicals that have benefits beyond basic nutrition. These latter substances are usually produced by plants as secondary metabolites to help in their defence against predator and pathogen attack. Chemically they're mostly polyphenols, grouped into several classes such as flavonoids (eg anthocyanins, flavones and flavonols), stilbenes, phenolic acids and tannins, and many have strong antioxidant activity. There are thousands of them and in numerous laboratory, animal and human studies they've been found to be effective agents in preventing or ameliorating cardiovascular disease, cancer, diabetes and mental degenerative diseases amongst others.
An important process by which these diseases develop concerns the production of reactive oxygen species associated with normal physiological activities. When these pro-oxidative states are not kept in check by the body's own antioxidants and those supplied externally from the diet, damage can occur over time. Recent research indicates that adequate intake of foods with phytochemicals high in antioxidants is a principal and significant means by which the above-mentioned diseases can be positively impacted. But as an aside it should be realised that antioxidant activity is not the only positive health attribute of plant phytochemicals; different fruits have widely varying mixtures of these chemicals with a multitude of activities and these are thought to interact positively in several ways. Focussing just on antioxidant activity as a major player in this story, berry fruit have on average 4, 10 and 40 times the activity of other fruits, vegetables and cereals respectively. Much of this is due to anthocyanins, which give them their characteristically strong orange, red and purple colours. Many hundreds of anthocyanins have so far been identified.
The following is a summary of work published in Nutrition Reviews (2010, 68, 168-177) where the case for including a hearty amount of berry fruit in your regular balanced diet is made.
Berries are a good source of polyphenols, especially anthocyanins, micronutrients, and fibre. In epidemiological and clinical studies these constituents have been associated with improved cardiovascular risk profiles. Human intervention studies using chokeberries, cranberries, blueberries, and strawberries (either fresh, or as juice, or freeze-dried), or purified anthocyanin extracts have demonstrated significant improvements in LDL-cholesterol oxidation (a precursor to blood vessel adhesion and atherosclerosis), lipid peroxidation, total plasma antioxidant capacity, dyslipidemia (high LDL-cholesterol and/or fats) and glucose metabolism. Benefits were seen in healthy subjects and in those with existing metabolic risk factors. Underlying mechanisms for these beneficial effects are believed to include up-regulation of endothelial nitric oxide synthase (increasing production of nitric oxide which favourably modulates blood pressure and blood vessel function), decreased activities of carbohydrate digestive enzymes, decreased oxidative stress, and inhibition of inflammatory gene expression and foam cell formation (scavenger cells containing numerous cholesterol droplets). Though limited, these data support the recommendation of berries as an essential fruit group in a heart-healthy diet.
This study by US researchers refers to several berry fruits from colder climates not readily available to us, but we can nevertheless take on board the findings for ones we do know well, such as strawberries, blueberries, and blackberries/raspberries and their many hybrids. Benefits extend beyond the cardiovascular disease largely addressed in the above study. For example in a recent Finnish study on the effects of including fruit, berries and vegetables in the diet, it was found that those in the top 25% of consumption had a reduced chance of developing diabetes after allowing for several other risk factors such as obesity, family history etc. Berries are usually eaten in much smaller quantities than other fruit and vegetables, yet when the effects of berries were considered separately from the other two in this comparatively small study, it was found that they alone were responsible for a 35% reduction in incidence and the other fruits and vegetables had no significant effect.
Another feature to consider with berries is the common practice of processing them into jams, jellies and the like. Unfortunately, these products may contain up to 50% added sugar to achieve good storage properties. Consumption then results in a rapid and unwanted extra increase in blood glucose and insulin which can be deleterious to health in the long term (eg predisposing to type 2 diabetes). The only saving grace here is that the berry polyphenols do have an ameliorating effect, but the better pathway to adopt is to either eat them fresh, freeze as purees, dry etc rather than add all that nutritionally-empty sugar to your diet. Collectively we're all eating too much as it is, and it's compromising the nutritional value of the berries which start off with such excellent credentials. And to top it all off, the antioxidant activity in the fresh fruit generally declines in proportion to any heat (time and temperature) processing steps.