Plant Based Whole Foods Diet Helps Respiratory Disease

In recent years, attention has focused on understanding how a westernized dietary pattern affects the lungs. The term 'westernized diet' is used to describe diets that are high in processed and 'fast foods', which are typically rich in saturated fat and simple carbohydrates, while being low in fruits, vegetables and wholegrains, which limit intake of dietary fibre and beneficial phytochemicals. Many chronic diseases, including cardiovascular disease, diabetes and some cancers, have been associated with this eating pattern, which is in complete contrast to healthy eating recommendations. ¹ More recently, respiratory researchers have been exploring whether this eating pattern also affects the lungs (Figure 1).

Dietary factors that influence the lungs. Westernized diets typically contain high amounts of processed and fast foods, whilst being low in fruits and vegetables. This dietary pattern has multiple components that modify airway inflammation, including but not limited to, low soluble fibre and antioxidant intake and excessive saturated fatty acid and energy intake, which leads to obesity. Correcting the balance to favour higher intake of fruits and vegetables is beneficial to the lungs

A growing body of evidence links different dietary components to lung inflammation. Excessive consumption of dietary fat, in particular saturated fat, leads to elevated circulating fatty acid levels. This can induce an inflammatory response by a variety of mechanisms, including activation of innate immune receptors, toll-like receptors (TLR) and endoplasmic reticulum stress. ² Systemic oxidative stress and inflammation resulting from fatty acid overload have been well described in both animals and humans. ² We now understand that excess fatty acids also affect the airways in the postprandial phase, with a high fat meal leading to increased induced sputum neutrophils and TLR4 gene expression, corresponding with an impaired bronchodilator response. ³

The role of dietary fibre in modulating inflammatory diseases via interaction with the gut microbiome is another emerging area which is relevant to lung health. A low fruit, vegetable and wholegrain diet leads to inadequate fibre intake, as dietary fibre is derived from plant-based foods. Fibre exists in soluble and insoluble forms, with soluble fibre being partially fermented by commensal bacteria as it passes through the colon, producing the short-chain fatty acids (SCFA), acetate, propionate and butyrate. SCFAs have anti-inflammatory actions via activation of free fatty acid receptors (G protein-coupled receptor [GPR] 41 and GPR43) and inhibition of histone deacetylases (HDACs). ² We have recently confirmed that these mechanistic pathways are relevant in human airways. One clinical study demonstrated that a single dose of the soluble fibre, inulin, activated sputum cell GPR41 and GPR43 and reduced inflammation in human airways, with a decrease in sputum neutrophils, sputum IL-8 and exhaled nitric oxide. ⁴ In another study, a 7-day inulin intervention led to an improvement in asthma control, decreased sputum eosinophils and decreased sputum cell HDAC9 gene expression. ⁵

Another consequence of inadequate fruit and vegetable consumption is low intake of antioxidants, which increases susceptibility to oxidative stress. Vitamin C, vitamin E and the carotenoids (including α- and β-carotene, lycopene and lutein) are all phytochemicals that demonstrate potent antioxidant properties and have been shown to be low in the circulation in asthma. ² While epidemiological data have linked dietary antioxidant status to lung health, ² antioxidant supplementation trials are unconvincing. ² The most promising strategy appears to be whole-food interventions, which simultaneously deliver a combination of nutrients which are likely to have interdependent roles that contribute to their beneficial effects.

Fruits and vegetables are an ideal whole-food intervention, as they deliver antioxidants and soluble fibre, as well as many other beneficial phytochemicals. Of relevance, the Food and Agriculture Organization of the United Nations has designated 2021 the International Year of Fruits and Vegetables (IYFV), in order to raise awareness of the important role of fruits and vegetables in human nutrition, food security and health. ⁶ Fruit and vegetable intake reduces systemic inflammation and risk of heart disease, stroke and cancer. ² Two clinical interventions have demonstrated that a high fruit and vegetable diet is also relevant in asthma. In a 10-day study, restricting fruit and vegetable intake to three serves per day led to an increase in sputum neutrophils, reduced lung function and worse asthma control. ⁷ Subsequently, two 7-day tomato-based treatments led to a reduction in neutrophil influx and activation in the airways. ⁷ In another 14-week study, adults who consumed a high fruit and vegetable diet (≥7 serves per day, equivalent to the Australian Dietary Guidelines) versus a low fruit and vegetable diet (<3 serves per day, equivalent to the median Australian intake) had a reduced risk of asthma exacerbation. ⁸ This study also highlights the benefits that could be gained by improving adherence to dietary guidelines.

Finally, lung health is strongly linked with obesity, which occurs as a result of excessive energy intake. The westernized dietary pattern is not only poor in quality, but also predisposes to the development of obesity, being high in energy-dense, nutrient-poor foods, while low in foods such as fruits and vegetables, which are an energy efficient source of beneficial nutrients. Obesity increases asthma risk and has many negative effects on lung health, including reduced lung function, reduced respiratory muscle strength, worse symptoms and reduced response to asthma pharmacotherapy. ² While we do not fully understand the mechanisms linking obesity and asthma, we do know that weight loss consistently leads to an improvement in lung health. A recent systematic review concluded that weight loss was associated with improvements in asthma-related quality of life, asthma control and lung function. ⁹ Furthermore, one study has demonstrated that achieving a threshold of just 5%–10% weight loss leads to clinically important improvements in asthma control and quality of life in the majority of asthmatic patients. ¹⁰ This highlights the importance of prioritizing weight loss to assist with the management of asthma in obese people.

In summary, substantial evidence describes the importance of dietary intake to lung health. The nutritional profile that results from a westernized diet has multiple components that are relevant to the airways, including but not limited to, excessive saturated fatty acid intake, low fibre and antioxidant intake and excess energy intake. A recent systematic review and meta-analysis concluded that fast food consumption was correlated with both asthma risk and wheeze in a dose-dependent manner, ¹¹ which is consistent with what we now know about the effects of nutrients on the lungs. Hence, the most useful dietary strategy that we have available is to adopt a healthy eating pattern, ¹ avoiding processed and fast foods, while increasing fruit and vegetable intake. This is a simple strategy for not only improving diet quality, but also achieving and maintaining a healthy weight, and is the best dietary approach for looking after the lungs.

CONFLICT OF INTEREST

The author has no conflict of interest to declare.

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Plant Based Whole Foods Diet Helps Respiratory Disease

Source: https://onlinelibrary.wiley.com/doi/full/10.1111/resp.14052

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