The Impact of Plant-Based Diets on Physical and Mental Health

Written by: Sarah Glinski, RD

Now more than ever, people are looking for ways to improve their physical and mental health. Diet is emerging as one of the strategies people can use to support their wellbeing. Many studies have found associations between diet and different aspects of physical health, and an emerging field of study called nutritional psychiatry is also starting to show associations between diet and mental health. Today, we’ll review some of the current evidence linking diet to physical and mental health so that you can provide evidence-based nutrition recommendations to your clients.

Plant-Based Diets and Physical Health

Many studies show the positive effects that a plant-based diet can have on health, including gut health,^1,2 diabetes prevention³ and treatment,⁴ and cardiovascular disease.⁶

Gut Health

Research shows that plant-based diets may promote the development of a more diverse and stable gut microbiota.¹ In particular, the polyphenols found in plant foods have been shown to increase populations of Bifidobacterium and Lactobacillus, which have been associated with anti-pathogenic and anti-inflammatory effects in the body.¹ Fibre consumption is also associated with an increase in these beneficial bacteria.²

High fibre intake has also been shown to benefit the gut through the production of short-chain fatty acids (SCFAs). Research has shown that SCFAs have many beneficial effects, including improved immunity, protection of the blood-brain barrier, and regulation of intestinal function.^1,2

Type 2 Diabetes

A systematic review and meta-analysis found that following a plant-based diet was associated with a lower risk of developing type 2 diabetes. When healthy plant-based foods such as fruits, vegetables, whole grains, legumes, and nuts were consumed, this effect was even more pronounced.³

Another systematic review that looked at the association between plant-based diets and type 2 diabetes management found that a plant-based diet was associated with significantly better HbA1C levels compared with other diets.⁴ HbA1C levels are a marker of blood glucose control, and a lowered HbA1C is associated with better diabetes control.⁵

Overall, encouraging a diet rich in plant-based foods can be an effective way to improve diabetes management and lower HbA1C.^3,4

Cardiovascular Disease

There are several components of plant-based diets that are associated with reduced risk of cardiovascular disease.

A review found that replacing saturated fats (which are predominantly found in animal products) with unsaturated plant fats (such as canola oil, olive oil, avocado oil, and nuts and seeds) was associated with a reduction in LDL-cholesterol, without affecting HDL-cholesterol and triglycerides. The review also found that in both observational and randomized control trials, replacing saturated fats with unsaturated plant fats was associated with a lower risk of cardiovascular disease.⁶

This review also found that the plant sterols found in plant foods (e.g. seeds, nuts, vegetables) were associated with significant reductions in LDL-cholesterol without significantly affecting HDL-cholesterol, however, to meet the recommended 2 g per day to benefit from the LDL-lowering effect, consumption must be supplemented with foods fortified with phytosterol (e.g. soft margarine and yogurt).⁶

Plant-Based Diets and Mental Health

The field of nutritional psychiatry is an emerging field of study that looks at the associations between diet and mental health.

Emerging data are starting to show an association between a poor diet and worsening symptoms of anxiety and depression. However, it’s important to note that current epidemiological data on the connection between nutrition and mental health have not yet revealed mechanisms by which nutrition affects mental health.⁷

A meta-analysis published in 2017 found that diets low in animal foods and high in vegetables, fruits, whole grains, fish (many of which are high in omega 3 fatty acids), olive oil, low-fat dairy, and antioxidants were associated with a reduced risk of depression.⁸

A randomized controlled trial called the “SMILES” (Supporting the Modification of lifestyle in Lowered Emotional States) trial looked at the effect of nutrition on moderate to severe depression. The nutrition group received counselling sessions with a registered dietitian, while the control group received social support counselling sessions. The study found that people receiving nutrition counselling had reduced symptoms of depression, and that they consumed more whole grains, fruit, low-fat and unsweetened dairy, olive oil, pulses, and fish.⁹

While the results of the studies looking at the relationship between mental health and nutrition are promising, it’s too early to say whether nutrition is an effective treatment for mental illnesses such as anxiety and depression.

An important point to consider is that observational studies do not demonstrate cause and effect. It’s quite possible that diet quality was negatively impacted by mental health symptoms, or that poor diet was associated with other factors that could affect mental health, such as socioeconomic status.

Overall, further research is needed to determine mechanisms by which nutrition might impact mental health.

Final Thoughts

While many studies show an association between markers of physical health and components of a plant-based diet, it’s still too early to recommend dietary interventions as a treatment for mental illness.

However, despite the evidence being in its infancy, eating regular, wholesome meals is an important act of self-care that people can engage in when they’re struggling with negative mental health symptoms.

By combining diet, exercise, and other evidence-based strategies, we can encourage our clients to pursue a holistic picture of wellness that considers more than just the physical aspect of health.

For tips on how your clients can get started with plant-based eating, plus other strategies for promoting overall wellness, check out our new guide “5 Steps to Whole-Body Health.”