The foods we consume on a daily basis have a profound impact on our health. Our daily nutrition is well-established as a leading risk factor in the development of obesity, cardiovascular disease and type 2 diabetes. The typical ‘Western diet’, awash in refined sugars, excess salt, white flour, processed meats, purified animal fats and food additives, contains low levels of dietary fibre, vitamins, minerals and antioxidants⁵; this diet promotes caloric excess and obesity, which impair immune function⁶. Eating in this way can impact immunity through a variety of mechanisms, including a reduced ability to respond to invading pathogens⁷, partially through having fewer and less potent white blood cells^8,9. 

While obesity remains a great public health concern in Australia, diets low in whole foods can produce nutrient deficiencies. Deficiencies in micronutrients including essential amino acids, folic acid, vitamins A, B6, B12, C and E, copper, iron and selenium can impair virtually all immune functions, making us more susceptible to infectious agents¹⁰. Consumption of these micronutrients at or above currently recommended levels is thus essential for the optimised function of our immune systems¹¹. Incorporating more fresh fruits, vegetables, nuts, seeds, whole grains and perhaps some lean fish and poultry, while minimising the intake of processed foods, remains sound dietary advice. Such diets also promote a healthy gut microbiome¹², which can enhance our defence mechanisms against invading pathogens¹³. While taking a deep dive into various dietary patterns and the claims around so-called ‘superfoods’ is beyond the scope of this article, we make a notable exception for the kiwifruit. It contains vitamin C, carotenoids, polyphenols and fibre, and has – in some intervention studies – been shown to reduce the incidence and severity of upper respiratory tract infections¹⁴. 

It is also worth noting the effect of diet on asthmatics, a population particularly at risk in the current moment. Asthmatics following a typical Western diet are at a higher risk of exacerbations – which can be triggered by viral infection – than those following a diet rich in fruit and vegetables.  In a three-month window, asthmatics who consumed 7 servings of fruits and vegetables a day had a 20% exacerbation rate, compared with 40% in those on a Western diet with just three servings of fruits and vegetables each day¹⁵.  Evidence from a randomised controlled trial suggests that these drastic improvements in exacerbation rates can be achieved after just fourteen days of increased fruit and vegetable consumption¹⁶. 

Finally, on a very interesting (and frightening) note, genetic studies using the coxsackievirus and influenza virus – two vastly different pathogens – have shown that virulence-enhancing mutations predictably occur when nutritionally compromised hosts are infected, particularly those with a deficiency in selenium and an excess in iron¹⁷. The benefits of eating well, then, extend beyond our individual responses and into the realm of the greater global community of humankind.