Low quality diets are increasingly being seen as a causative factor in disease progression and ill health. Low quality diets tend to be those with high total energy, and contain foods characterised by high concentrations of refined carbohydrates and non-essential fat, along with low concentrations of micronutrients. Low quality diets tend to contain mainly highly processed pre-prepared foods with poor micronutrient to energy ratios. In contrast, high quality diets are characterised by high intakes of fruits, vegetables, fibre, whole grain cereals and micronutrient dense energy poor foods, with minimal processing or heating. Despite these general classifications, there is no official consensus on what constitutes diet quality, although diets such as the Mediterranean diet are thought of as high quality in nutritional research. The Mediterranean diet has high levels of antioxidants and this might be one reason for the health benefits associated with adherence to the diet.
In an attempt to quantify the quality of diets, researchers have measured the total antioxidant capacity of foods, and assessed the associations with other possibly diet quality characteristics such as the energy density of the food and predefined nutritional quality index. To achieve this, dietary records were used to assess the total antioxidant capacity of the diet in 153 young adult participants. From the data, positive associations were identified between the total antioxidant capacity of the diet and various dietary indexes which rate the quality of the foods against diets such as Mediterranean diet, Alternative Healthy Eating Index and Healthy Eating Index. The researchers also reported an inverse relationship between the total antioxidant capacity of the food and its energy density. The total antioxidant capacity of the diet therefore appears to be a useful measure of the diet quality, and shows associations with known high quality diets.
It is unknown which antioxidants in plants are most beneficial to the health, but much research has attempted to elucidate the in vivo antioxidant effects of various plant foods. The Carotenoids and flavonoids are the most heavily researched plant antioxidants. and strong evidence suggests a role for these compounds in disease prevention. Other dietary antioxidants such as vitamin E and vitamin C undoubtedly play a role in health. While much of the research studies have attempted to understand the effects of single antioxidants, less time has been spent researching the synergistic effects of a number of antioxidants. Synergism is likely important between antioxidants of different classes, and this can be illustrated by the health benefits of red wine. Red wine is a complex mixture of many antioxidant compounds, and although not fully characterised, studies attest to the benefits of both red wine in the prevention of cardiovascular disease.
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