Postprandial metabolic events and fruit-derived phenolics

"Eat to Live, Not Live to Eat"
John H Weisburger, 2000

Most people are aware of the term ‘Glycemic Index' (GI) which can be applied to different foods.  Essentially it gives an indication of how rapidly the glucose component of a food is absorbed in the body relative to glucose itself.  High GI foods produce very fast and high peak blood levels of glucose, whereas those with low GI produce lower and more gradual elevation.  In the former situation there is a correspondingly rapid and large rise in insulin blood level, that if continued over many years can result in insulin resistance, diabetes and other negative health outcomes.  Recommendations to eat foods with low GI minimise this outcome and allow glucose and insulin to quickly return to the base-line state.  Minimally processed plant-based foods such as fruit and vegetables with their high fibre content can slow absorption of glucose from the food matrix and help achieve this goal.

A similar high peak in blood lipids occurs after meals containing foods with significant fat content.  Again, the preferred outcome is to have slower longer absorption with less severe disruption of the resting state, and fibre contained in fruit and vegetables can assist here also.  Elevated lipid, glucose and insulin levels after food represent pro-oxidant and pro-inflammatory stressors but in a healthy person these effects are kept in balance by anti-oxidant chemicals in food and in the body.  If not counteracted by antioxidants then, for example, LDL-cholesterol (the bad cholesterol) can become oxidised and it is then more likely to attach to the interior walls of arteries, leading on to atherosclerosis and cardiovascular disease.  It is in provision of antioxidants that there is a distinction between fresh fruit and vegetables, as fruit contain on average several times the antioxidant levels as vegetables.  Also, because many vegetables are not very palatable in the raw state they are usually processed in some way before eating, and this can lead to varying levels of antioxidant loss or degradation, further accentuating the differences.

There is now overwhelming epidemiological evidence for the general value of fruit and vegetables in minimising the chronic diseases that are all too common in Western countries.  What the study below examines is whether these beneficial effects are independent of when they're consumed with respect to other foods, or are they more effective when taken with meals (British Journal of Nutrition (2010), 104, S1–S14).

There is increasing evidence that the postprandial (after meal) state is an important contributing factor to chronic disease.  This review assesses the role of fruit phenolic (antioxidant) compounds to protect health and lower disease risk through their actions in mitigating fed-state metabolic and oxidative stressors.  Two main questions are posed: first, what is the role of plant foods, specifically fruits rich in complex and simple phenolic compounds in postprandial metabolic management; and second, does the evidence support consuming these fruits with meals as a practical strategy to preserve health and lower risk for disease?

An overview of the postprandial literature is presented, specifically on the effect of fruits and their inherent phenolic compounds in human subjects on postprandial elevated blood lipids, glucose and insulin, and associated events such as oxidative stress and inflammation.  Among the identified well-controlled human trials using a postprandial paradigm, half used wine or wine components and the remaining used various berries.  Notwithstanding the need for more research, the collected data suggest that consuming phenolic-rich fruits increases the antioxidant capacity of the blood, and when they are consumed with high fat and carbohydrate ‘pro-oxidant and pro-inflammatory' meals, they may counterbalance their negative effects.  Given the content and availability of fat and carbohydrate in the Western diet, regular consumption of phenolic-rich foods, particularly in conjunction with meals, appears to be a prudent strategy to maintain oxidative balance and health.

If you're in the habit of having a dessert after dinner, you could be doing yourself a big favour down the track if you substitute fresh fruit for the more indulgent ice-cream, cheese cake etc.  And what about a fruit salad or smoothie to go along with the rest of your lunch?  Fruit will not only address the antioxidant story above but also add into the deal their high fibre content and low calories.

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