Just as the effect of diet on a single biomarker may be insufficient evidence to assess coronary heart disease risk, the effect of a single macro- or micronutrient may be insufficient evidence to assess risk of all-cause mortality.

An abundance of literature exists pertaining to specific nutrients and their effect on health, especially fats; however, it would be prudent that we pay increased attention to our diet as a whole and the balance of foods within. Thus, extending past such limited approaches as explicitly recommending low fat or low carbohydrate diets, it may be shrewd of research and individuals to modernise their dietary focus, questioning the effects of individual foods and the combinatory influence of the ‘whole diet’.

The aforementioned push for modernisation is adequately summed up by Ms Catherine Collins (Principal Dietitian at St George’s Hospital NHS Trust), following her comments regarding a published research review claiming that recommendations on dietary fat intake in the UK and US are completely unfounded: “Finally, this review reminds us that like Saturday Night Fever, tartan culottes and bubble perms, the reductionist ‘single nutrient’ dietary recommendations deserve to be left in the early 80’s where they belong. As do doctors and other health professionals who persist in their persecution of single nutrients whilst ignoring a ‘whole diet’ approach.”

Around the same time as the above publication I stumbled across an article claiming ‘Brazil has the best nutritional guidelines in the world’. While a hefty claim there’s valid reason for such a claim: these guidelines are incredibly practical! Brazil’s guidelines focus on meals, emphasising such simple concepts as making natural or minimally processed foods the basis of your diet i.e. consume water, milk, and fruits rather than soft drinks, dairy drinks, and biscuits; beneficial methods of food preparation i.e. roasting, grilling, sauteing red meat; and foods influence on health i.e. fruits are an excellent source of dietary fibre, vitamins and minerals, and several compounds that contribute to the prevention of many diseases.

Unfortunately, nutritional research is dominated by the archaic single nutrient focus. However, as I intend to highlight below, present research pertaining to the whole diet approach and individual foods offer interesting, and somewhat contradictory observations in comparison to single nutrient studies. Consequently, such contradiction could be seen to advise that nutritional research apply increased consideration towards the potentially synergistic effects of a food’s macronutrients, micronutrients and bioactive components.

The benefits of the whole diet approach are best exemplified by the Mediterranean Diet. The Mediterranean dietary pattern features a high intake of olive oil, olives, legumes, whole grains, vegetables, and fruit, moderate intake of fish, low-to-moderate intake of dairy products (primarily cheese and yogurt), moderate intake of wine with meals, and a low intake of red and processed meat. Adherence to this dietary pattern, and modified variants, regularly confers an inverse association with incidence of disease, including metabolic syndrome (a cluster of metabolic risk factors associated with increased risks of cardiovascular disease and type 2 diabetes; including such components as abdominal obesity, hyperglycaemia, hypertension, and dyslipidemia). This beneficial relationship may arise due to the nutritional diversity encountered with the Mediterranean diet. Specifically, this dietary pattern includes foods and beverages that are rich in a myriad of nutrients, including monounsaturated fat, antioxidants, fibre, calcium, magnesium, and phytoestrogens (Steffen et al. 2014).

Relating to the components of the Mediterranean diet:

  • Inverse associations have been reported between whole-grain foods and glucose concentrations, insulin resistance and incident diabetes – potential contributions to improvements of the metabolic profile are suggested as being related to the content of such components as dietary fibre, inulin, β-glucan, resistant starch, phenolics, tocotrienols, tocopherols, and carotenoids (many of which exhibit antioxidant activities) (Suliga et al. 2015).
  • Moderate alcohol intake has been reported to be associated with higher HDL (“good”)-cholesterol concentrations (Steffen et al. 2014).
  • Blood pressure may be beneficially modulated by intakes of fruit and vegetables that are rich in potassium, fibre, and antioxidants, while intakes of plant protein and foods from plant sources are inversely associated with blood pressure (Steffen et al. 2014).
  • Meat intake has been reported to be positively associated with blood pressure and risk of hypertension in populations; numerous studies have also shown positive associations between red and processed meat intake and adiposity and type 2 diabetes (Steffen et al. 2014).
  • Finally, fish intake has been reported to be inversely associated with cardiovascular disease (CVD) risk factors and the metabolic syndrome and its individual components – typically attributed to the consumption of unsaturated fatty acids, eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA). Moreover, fish contains vitamin D, calcium and high-quality proteins, which may also affect disease risk (Zaribaf et al. 2014).

The adverse effects of red meat are often associated with saturated fat content, inversely associated with cholesterol, blood pressure, obesity, and diabetes risk (Babio et al. 2012); however, emerging research surrounding dairy products – typically high in saturated fat content – potentially indicates that additional components are at play. The debate surrounding dietary fat continues with dairy products, emphasised by the rather enigmatic difference towards health when comparing low-fat and full-fat dairy products: Dietary Approaches to Stop Hypertension (DASH) has shown that substantial blood pressure reductions can be achieved when low-fat dairy products were added to a healthy food and vegetable diet (Goldbohm et al. 2011). Whereas consumption of fermented full-fat milk shows a small, but consistent, inverse and statistically significant association with mortality; fermented milk products, particularly yogurt, may exert beneficial probiotic effects, potentially enhancing the immune response and increased resistance to immune-related diseases (Astrup 2014, Crichton & Alkerwi 2014).

Definitively, benefits associated with dairy products may be food specific. For instance, in one study, milk, yogurt, and cheese intakes – but not dairy desserts, ice cream, or butter – were associated with better cardiovascular health (Crichton & Alkerwi 2014). Anyhow, multiple possible mechanisms have been postulated for the observed benefits: Regardless of fat content, calcium could increase fat oxidation (inducing thermogenesis), lipolysis and faecal fat loss (assisting in decreased cholesterol levels) and could help in appetite control. Calcium also exhibits blood pressure lowering effects by decreasing vascular resistance and sodium retention. However, it may be apt to note that when fat content is lower the beneficial impact of calcium may be more obvious, potentially leading to lower LDL (“bad”)-cholesterol levels. Furthermore, whey proteins – present in dairy – may inhibit the angiotensin-converting enzyme, which has a proven role in blood pressure management. Dairy proteins also suppress short-term food intake, increase satiety (inhibition of the hunger drive), and stimulate food intake regulatory mechanisms known to signal satiation (feeling of fullness) and satiety (Huo Yung Kai et al. 2014). It’s also possible that the presence of magnesium reduces blood pressure and vitamin D improves endothelial function (Benatar et al. 2014).

In addition to dairy products, further examples of specific foods with suggested health benefits exist:

  • Evidence suggests that fish oil intake may improve dyslipidemia by lowering blood triglycerides and elevating HDL-cholesterol levels (Baik et al. 2010).
  • A meta-analysis on 13 prospective cohort studies reported that each 20g increase in daily fish intake was associated with a 7% lower risk of coronary heart disease mortality (Baik et al. 2010).
  • A study in Korea reported that risk of metabolic syndrome increased among people eating white rice compared with those eating rice with beans and rice with multi-grains (Aekplakorn et al. 2015).
  • Fibre from cereal sources has a strong inverse association with the risk of cardiovascular disease and diabetes (Hosseinpour-Niazi et al. 2015).
  • Fruit fibre reduces concentrations of inflammatory factors such as C-reactive protein and TNF-α, which may prevent or delay the development of metabolic syndrome (Hosseinpour-Niazi et al. 2015).
  • Intake of tree nuts and peanuts, but not peanut butter, is inversely related to mortality. When comparing peanuts with walnuts, both are good sources of magnesium, monounsaturated fatty acids (MUFA) and polyunsaturated fatty acids (PUFA), but walnuts contain more alpha-linolenic acid; peanuts are richer in MUFA, protein, niacin and potassium. Both peanuts and walnuts are sources of phytosterols, that inhibit colon, prostate and breast cancer cells in vitro, and are implicated in cardiovascular disease because of their cholesterol reducing action. Additionally, peanuts, along with grapes and red wine, are primary sources of resveratrol, which is suggested to reduce chronic disease risk. However, differences in mortality associations between peanuts and peanut butter may be due to the addition of partially hydrogenated vegetable fats (trans fats) to peanut butter (van den Brandt & Schouten 2015).

Conclusively, there’s a notable discordance between nutrient, food and dietary-based associations with health. Research has repeatedly hypothesised the key role of saturated fatty acids in relation to diet and disease risk, with the totality of evidence indicating such conclusions as substituting polyunsaturated fatty acids for saturated fatty acids is beneficial for lowering total- and LDL-cholesterol and for coronary heart disease prevention (Astrup et al. 2011); however, nutrients are ingested as complex mixtures in foods, which are consumed as mixed meals and diets. The biological effects of a nutrient in a food may be altered through interaction with other constituents within the food or other foods in the overall diet. Thus, in the future, guidelines and considerations based on foods, food groups and ultimately whole diets, may offer a more rational and comprehensive approach for reducing disease risk and total-mortality. However, the development of a stronger, less limited research base is required.