Food as medicine: your brain really does want you to eat more veggies



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Diet reduces risk of depression through actions on bacteria in the gut, the immune system and the brain.
from www.shutterstock.com

Felice Jacka, Deakin University

This article is part of a three-part package “food as medicine”, exploring how food prevents and cures disease. Read other articles in the series here. The Conversation


As well as our physical health, the quality of our diet matters for our mental and brain health. Observational studies across countries, cultures and age groups show that better-quality diets – those high in vegetables, fruits, other plant foods (such as nuts and legumes), as well as good-quality proteins (such as fish and lean meat) – are consistently associated with reduced depression.

Unhealthy dietary patterns – higher in processed meat, refined grains, sweets and snack foods – are associated with increased depression and often anxiety.

Importantly, these relationships are independent of one another. Lack of nutritious food seems to be a problem even when junk food intake is low, while junk and processed foods seem to be problematic even in those who also eat vegetables, legumes and other nutrient-dense foods. We’ve documented these relationships in adolescents, adults and older adults.

Diet has an impact early in life

The diet-mental health relationship is evident right at the start of life. A study of more than 20,000 mothers and their children showed the children of mothers who ate an unhealthier diet during pregnancy had a higher level of behaviours linked to later mental disorders.

We also saw the children’s diets during the first years of life were associated with these behaviours. This suggests mothers’ diets during pregnancy and early life are both important in influencing the risk for mental health problems in children as they grow.

This is consistent with what we see in animal experiments. Unhealthy diets fed to pregnant animals results in many changes to the brain and behaviour in offspring. This is very important to understand if we want to think about preventing mental disorders in the first place.

Teasing out the cause from the correlation

It’s important to note that, at this stage, most of the existing data in this field come from observational studies, where it is difficult to tease apart cause and effect. Of course, the possibility that mental ill health promoting a change in diet explains the associations, rather than the other way around, is an important one to consider.

What comes first, the junk food or the depression?
from shutterstock.com

Many studies have investigated this and largely ruled it out as the explanation for the associations we see between diet quality and depression. In fact, we published a study suggesting that a past experience of depression was associated with better diets over time.

But the relatively young field of nutritional psychiatry is still lacking data from intervention studies (where study participants are given an intervention that aims to improve their diet in an attempt to affect their mental health). These sorts of studies are important in determining causality and for changing clinical practice.

Our recent trial was the first intervention study to examine the common question of whether diet will improve depression.

We recruited adults with major depressive disorder and randomly assigned them to receive either social support (which is known to be helpful for people with depression), or support from a clinical dietitian, over a three-month period.

The dietary group received information and assistance to improve the quality of their current diets. The focus was on increasing the consumption of vegetables, fruits, wholegrains, legumes, fish, lean red meats, olive oil and nuts, while reducing their consumption of unhealthy “extra” foods, such as sweets, refined cereals, fried food, fast food, processed meats and sugary drinks.

The results of the study showed that participants in the dietary intervention group had a much greater reduction in their depressive symptoms over the three months, compared to those in the social support group.

At the end of the trial, 32% of those in the dietary support group, compared to 8% of those in the social support group, met criteria for remission of major depression.

These results were not explained by changes in physical activity or body weight, but were closely related to the extent of dietary change. Those who adhered more closely to the dietary program experienced the greatest benefit to their depression symptoms.

While this study now needs to be replicated, it provides preliminary evidence that dietary improvement may be a useful strategy for treating depression.

Depression is a whole-body disorder

It’s important to understand researchers now believe depression is not just a brain disorder, but rather a whole-body disorder, with chronic inflammation being an important risk factor. This inflammation is the result of many environmental stressors common in our lives: poor diet, lack of exercise, smoking, overweight and obesity, lack of sleep, lack of vitamin D, as well as stress.

Many of these factors influence gut microbiota (the bacteria and other microorganisms that live in your bowel, also referred to as your “microbiome”), which in turn influence the immune system and – we believe – mood and behaviour.

In fact, gut microbiota affect more than the immune system. New evidence in this field suggests they are important to almost every aspect of health including our metabolism and body weight, and brain function and health. Each of these factors is relevant to depression risk, reinforcing the idea of depression as a whole-body disorder.

What is the human microbiome?

If we do not consume enough nutrient-dense foods such as fruits, vegetables, fish and lean meats, this can lead to insufficiencies in nutrients, antioxidants and fibre. This has a detrimental impact on our immune system, gut microbiota and other aspects of physical and mental health.

Gut microbiota are particularly reliant on an adequate intake of dietary fibre, while the health of the gut may be compromised by added sugars, fats, emulsifiers and artificial sugars found in processed foods.

A diet high in added fats and refined sugars also has a potent negative impact on brain proteins that we know are important in depression: proteins called neurotrophins. These protect the brain against oxidative stress and promote the growth of new brain cells in our hippocampus (a part of the brain critical for learning and memory, and important to mental health). In older adults we have shown that diet quality is related to the size of the hippocampus.

Now we know diet is important to mental and brain health as well as physical health, we need to make healthy eating the easiest, cheapest and most socially acceptable option for people, no matter where they live.


Further reading:

Food as medicine: why do we need to eat so many vegetables and what does a serve actually look like?

Felice Jacka, Principal Research Fellow, Deakin University

This article was originally published on The Conversation. Read the original article.

Food as medicine: why do we need to eat so many vegetables and what does a serve actually look like?


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Why do we need so many serves of vegetables in a day?
Unsplash/Jonathan Pielmayer, CC BY-SA

Genevieve James-Martin, CSIRO; Gemma Williams, CSIRO, and Malcolm Riley, CSIRO

This is the first article in a three-part package “food as medicine”, exploring how food prevents and cures disease. The Conversation


Most Australian adults would know they’re meant to eat two or more serves of fruit and five or more serves of vegetables every day. Whether or not they get there is another question.

A recent national survey reported 45% of Australian women and 56% of Australian men didn’t eat enough fruit. And 90% of women and 96% of men didn’t eat enough vegetables. This figure is worse than for the preceding ten years.

Men had on average 1.6 serves of fruit and 2.3 serves of vegetables per day, and women had 1.8 serves of fruit and 2.5 serves of vegetables. A serve of fresh fruit is a medium piece (about 150 grams) and a serve of vegetables is half a cup of cooked vegetables or about a cup of salad.


The Conversation/Australian Dietary Guidelines, 2013, CC BY-ND

Why do we need so many veggies?

A high intake of fruit and vegetables lowers the risk of type 2 diabetes, heart disease, stroke and some cancers. These chronic diseases are unfortunately common – it’s been estimated A$269 million could have been saved in 2008 if everyone in Australia met fruit and vegetable recommendations.

The recommendation to include plenty of vegetables and fruit in our diet is based on a large body of evidence showing the risk of a range of health conditions is reduced as we eat more fruit and vegetables. The specific targets of two serves for fruit and five to six serves for vegetables are largely based on nutrient requirements for healthy people and what diets usually look like for the average Australian.

So to set these guidelines, certain assumptions are made about dietary practices, such as breakfast being based around cereal/grain and dairy foods, and main meals being comprised of meat and vegetables, usually with a side of something starchy like rice, pasta or the humble potato – an Australian staple.

Does this mean it’s the only pattern to meet all the nutrient requirements? No. Could an adult be equally healthy if they ate three serves of fruit and four serves of vegetables? Yes, probably.

Some recent research even suggests our current targets don’t go far enough. It estimates an optimal intake for reducing our risk of heart disease and early death to be around ten serves of fruit and vegetables a day. Whether we are aiming for two and five, or ten serves, is somewhat academic – the clear message is most of us need to increase our fruit and vegetable intake.

Aussies eat more potatoes than any other veggie.
Agence Producteurs Locaux Damien Kühn/Unsplash, CC BY

Why is two and five such a hard ask?

The populations of most Western countries report eating far less fruit and vegetables than they’re supposed to. So what’s making it so hard for us to get to two and five?

Diets higher in fat, sugar and grains are generally more affordable than the recommended healthy diets high in fruit and veg. In fact, for Australians on low incomes, a healthy food basket for a fortnight would cost 28 to 34% of their income, up to twice the national average for food expenditure.

As a result, people with limited access to food for financial reasons often choose foods with high energy content (because they are filling) over those with high nutritional value but low energy content like fruit and vegetables. These high-energy foods are also easy to over-consume and this may be a contributing factor to weight gain. People who are poorer generally have a diet poorer in quality but not lower in energy content, which contributes to a higher rate of obesity, particularly in women.

Fresh fruit and vegetables cost more to purchase on a dollars per kilojoule basis, and also perish more quickly than processed foods. They take more time and skill to prepare and, after all of that effort, if they don’t get eaten for reasons of personal preference, they go to waste. For many it may not stack up financially to fill the fridge with fruit and vegetables. Under these circumstances, pre-prepared or fast food, which the family is sure to eat without complaint or waste, is all too convenient.

How we can increase veggie intake

The home and school environments are two key influencers of children’s food preferences and intakes. Parents are the “food gatekeepers” and role models particularly for younger children. Where there is parental encouragement, role modelling and family rules, there is an increased fruit and vegetable intake.

Dietary behaviours and food choices often start in childhood and continue through adolescence to adulthood. So encouraging fruit and vegetable intake in schools by mechanisms such as “fruit snack times” may be a good investment.

Policy approaches include subsidies on healthy foods. Other examples include levying a tax on foods of low nutritional value, improved food labelling, and stricter controls on the marketing of unhealthy foods. In Australia debate continues around a tax on sugar-sweetened beverages, which could be used to subsidise healthy foods such as fruit and vegetables.

Research has found the more variety in fruit and vegetables available, the more we’ll consume. Those who meet the vegetable recommendation are more likely to report having at least three vegetable varieties at their evening meal. So increasing the number of different vegetables at the main meal is one simple strategy to increase intake.

This could be made a journey of discovery by adding one new vegetable to the household food supply each week. Buying “in season” fruit and vegetables and supplementing fresh varieties with frozen and canned options can bring down the total cost. Then it’s a matter of exploring simple, quick and tasty ways to prepare them so they become preferred foods for the family.

Genevieve James-Martin, Research Dietitian, CSIRO; Gemma Williams, Research Dietitian, CSIRO, and Malcolm Riley, Nutrition Epidemiologist, CSIRO

This article was originally published on The Conversation. Read the original article.