Diet and Disease

Of all the documented benefits of plant-based diets, perhaps the most famous are those regarding cardiovascular disease (CVD) and it’s risk factors. As CVDs contribute to huge morbidity and mortality in our society, the benefits in this context also have the potential to be the most revolutionary for modern healthcare.

CVD includes heart attacks and strokes, with its risk factors including high cholesterol, high blood pressure (hypertension) and diabetes (the latter of which is also considered a separate disease entity and will be considered in more detail below).

Large amounts of research has shown that diets containing animal based products, and mainly foods containing high levels of saturated fats such as red meat and dairy, have an increased risk of many individual risk factors of cardiovascular disease, as well as an increased risk of CVD as a whole.^{5, 6}

In order to understand this link, it is important to understand that CVD is caused by the effects of hypertension, high cholesterol and diabetes on the walls of blood vessels, and the subsequent development of plaques in these blood vessels, which can then occlude blood supply to the heart or brain. Other risk factors independent of diet such as smoking, genetics and ethnicity can also contribute to this process.

Plant-based diets have been proven to lower blood pressure, lower cholesterol, induce remission in non-insulin dependent diabetes, and subsequently decrease the propensity for plaques to form and occlude blood vessels.^7-10 In this way, plant-based diets have been shown to reduce the risk of CVD by 40%. As well as preventing CVD through the treatment of these risk factors, plant-based diets can also be therapeutic in reducing the amount of plaque in people who already have disease, and subsequently their risk of future heart attacks.¹¹

When you consider that the medical treatments for the above conditions, though effective, are at best multiple medications and at worst open heart surgery, wouldn’t simply trying a plant-based diet be a preferable treatment option?

Diabetes is a disease where the body is not able to regulate the amount of sugar in the blood. Whilst carbohydrates can contribute to high blood sugar levels once a person has developed diabetes, the development of adult diabetes seems to be more related to fat consumption, which decreases the effect of an important hormone called insulin. Diabetes has many complications, including heart attacks, strokes, kidney failure (which sometimes requires dialysis), blindness, decreased blood supply and decreased nerve sensation – the latter two often resulting in non-healing wounds of the toes and feet that require amputation.

People who eat a plant-based diet have a substantially lower risk of developing adult diabetes.¹⁵ Furthermore, type 2 diabetes, otherwise managed with medications or injecting insulin, has been shown to be treatable with a plant-based diet, with people achieving greater diabetic control and less diabetic complications than with a standard animal-based diet.^{16, 17}

It is important to note that insulin dependent diabetes, previously known as type 1 diabetes, is unable to be managed only by dietary control, and it is very important for these patients to continue to adhere to an insulin regime advised by an endocrinologist, regardless of the diet they consume.

We currently live in an aging population, and as the health conditions associated with aging are resource intensive for the healthcare system, a low-cost intervention such as dietary change could play a major role in reducing the suffering and burden of disease associated with neurodegenerative conditions.  

Though our understanding of dementia is still evolving, there is now substantial evidence that has linked all subtypes of dementia to cardiovascular disease and diabetes. Indeed, these studies are showing that the risk factors for cardiovascular disease and cognitive decline are the same, and as such, modifications that work for cardiovascular disease may very well work for dementia.¹⁸

Indeed, in 2013, at the International Conference on Nutrition and the Brain, experts came up with seven recommendations for the prevention of dementia, of which the following was included: Vegetables, legumes (beans, peas, and lentils), fruits, and whole grains should replace meats and dairy products as primary staples of the diet.¹⁹Though we do not fully understand the mechanism by which this link exists, it has been hypothesised that the damaging saturated and trans-fats found in large quantities in meat and dairy products are the culprit, and cause increased inflammation and decreased cellular regeneration throughout the body.²⁰

Though cancer continues to have a devastating effect on the lives of many people, due to huge medical advances it is no longer the impossible condition to treat that it once was. As our understanding of cancer and how to target it increases, it is becoming clearer that some cancers may be preventable – for example, in the case of lung cancer, which is very positively associated with the modifiable risk factor of smoking. In fact, it is now estimated that 30-50% of all cancers are preventable through healthy diet and lifestyle, with a plant-based diet showing a decrease in total cancer risk.²¹ Indeed, even in omnivorous diets, those which contain more plants and less meat have a decreased risk of developing cancer overall.²² This evidence is now so well-demonstrated that the World Cancer Research Fund recommends a diet with more plants and less red and processed meats for the prevention of cancer.²³

The cancers which seem to be most influenced by diet include bowel cancer, breast cancer and prostate cancer. In regards to bowel cancer, it has been well publicised that the World Health Organisation (WHO) has classified processed and red meats as type 1 and 2 carcinogens; that is that they either have been proven carcinogenic or are likely carcinogenic respectively. It is important to note that this classification does not assess the level of risk of a carcinogen, and it would be false to purport that meat has as great a carcinogenic effect as, for example, tobacco (another type 1 carcinogen).

As with total cancer, breast cancer has been shown to be positively associated with diets containing more meat and less plants, and there is a growing body of evidence that adherence to a plant-based diet may protect against breast cancer.²⁴Likewise with prostate cancer, eating more plants confers a decreased risk of developing prostate cancer, whereas specifically a higher dairy intake is associated with a higher risk of developing prostate cancer.^{25, 26} Furthermore, plant-based diets have been shown to have a therapeutic effect on prostate cancer, decreasing the rate at which the disease progresses.^{27, 28}

Chronic kidney disease (CKD), though less famous than other chronic diseases, is also a huge contributor to morbidity and mortality in our society. As we age our kidney function decreases, and this process can be accelerated by high blood pressure, diabetes and high cholesterol. People with CKD are prone to electrolyte imbalances, which can make them quite unwell, and at later stages require kidney function replacement in the form of dialysis – a machine that replaces the kidneys in their role of filtering blood.

Historically, plant-based diets were thought to be nutritionally inadequate for people with CKD as it is important for these patients to replenish protein lost through their urine. However newer research indicates this is not the case.²⁹ In fact, plant-based diets confer a decreased risk of first developing CKD, and then also slow the progression of the disease after it has developed, possibly through intrinsic reno-protective properties of plant-based foods (still being researched) and also by addressing the risk factors that contribute to CKD itself.^30-33 Furthermore, plant-based diets are associated with a decreased all-cause mortality in patients with CKD.³⁴ 

It is important to note that while plant-based diets can be appropriate for early stages of CKD, in late stage CKD it is important to limit the dietary intake of potassium and phosphate, which can easily accumulate to dangerous levels in the blood without a well-functioning filtration system, and in these situations plant-based diets require careful consideration. Anyone with end-stage kidney disease should have a renal physician and dietician, and be guided by their recommendations prior to commencing on a plant-based diet.

Rheumatoid arthritis (RA) is an often debilitating autoimmune joint condition, which is still poorly understood. Though there are many unmodifiable risk factors associated with RA, it has also been well documented that certain foods often trigger worse joint pain in those affected. Although these foods remain individualised for each person, plant-based diets cut out many common trigger foods, and have shown to improve the symptoms of RA, possibly through a role in improving gut bacteria composition and subsequently decreasing inflammation.³⁵ Further research is needed in this area to further characterise the effects plant-based diets may have on the morbidity associated with RA. 

Asthma is a chronic respiratory condition characterised by reversible narrowing and inflammation of airways, which can often be devastating in children. Preliminary research has shown, through the effects on systemic inflammation, oxidation and microbial composition, eating more vegetables and less animal products (particularly dairy) can result in less risk of developing asthma as well as better control of existing asthma.^36-38 Again, further research is required in this domain before definitive conclusions can be made.

At this point in this article you may be wondering how a single diet can have so many varied effects on health. Indeed, though we have seen the positive effects of plant-based diets, the mechanism by which they occur is still being investigated by the scientific community. One hypothesis for which there is increasing evidence is that plant-based diets can change our gut microbiome to be more diverse and protective. This is important as we are learning more and more that the bacteria in our gut can have systemic effects on our bodies – for example, diets high in animal products have a higher proportion of gut bacteria which are pathogenic and promote inflammation, whereas the opposite is true for plant-based diets. Though much more research into this area is required, this hypothesis could very well be the link between metabolism of diet and chronic health diseases that would provide evidence at a cellular level of how diet can influence disease.^39-41

Is a plant-based diet safe in pregnancy, breastfeeding and childhood?

Despite common misconceptions, plant-based diets have been shown to be completely safe during pregnancy, lactation and childhood as long as all nutritional requirements are met, as is stated in the official Australian Dietary Guidelines. Though many people can easily achieve this, it should be noted that some people may need to take special care and a little extra planning to maintain their nutritional requirements during these phases of the lifecycle.^{42, 43}

Don’t I need meat to be competitive as an athlete?

There is no evidence that plant-based athletes are at a disadvantage compared to athletes who eat animal products. In fact, there are certain theoretical biological mechanisms by which plant-based diets may actually be beneficial for athletes – including reducing body fat, increasing glycogen storage, improving vascular flow to muscles and decreasing inflammation in the body.^{44, 45} Plant-based athletes include the world-record holding strongman, record-holding weightlifters and ultramarathoners, as well as well-known names such as Novak Djokovic and Patrik Baboumian.

But isn’t meat a complete source of protein?

While it is true that meat contains all essential amino acids, it is a myth that it is impossible or even difficult to meet adequate protein requirements with a plant-based diet. Indeed, as long as people are eating a varied diet which includes some plant-based protein foods (tofu, beans/legumes, nuts/seeds), and meeting their daily energy intake requirements, it is actually very difficult to be protein deficient.⁴⁶

Don’t I need milk to have strong bones?

While milk is a source of calcium, there are also many plant-based sources of calcium which additionally have intrinsic protective effects on bones, as well as confer less risk of chronic disease than dairy products do. This has been validated by studies which show that there is no increased risk of fractures or osteoporosis with plant-based diets, unless there is a marked deficiency in calcium. Calcium deficiency in people who maintain a healthy plant-based diet is uncommon, however it is possible in those who have an unhealthy plant-based diet and as such vegans should be aware of it as a potential “shortfall” nutrient.^47-49

Is it necessary to supplement vitamin B12 in a vegan diet?

Vitamin B12 is made through the conversion of cobalt by bacteria. These bacteria are found in soil, algae and in the digestive tracts of ruminant animals. Though there are a few plant-sources of vitamin B12, it is unsafe to exclusively rely on these for adequate intake of vitamin B12. It is recommended that anyone who consumes a plant-based diet takes vitamin B12 supplements and chooses foods fortified with vitamin B12, which are safe and widely used; in fact, most livestock is actually supplemented with vitamin B12 themselves.

I am a man, can’t the oestrogens in soy affect my testosterone levels?There are no bioequivalent forms of the human sex hormone oestrogen found in soy. What is in soy are chemicals called phytoestrogens, which possess a chemical structure similar to that of endogenous human oestrogen. As such, they can bind to oestrogen receptors, however they have a very low affinity to do so, and if they do they can produce either oestrogenic, anti-oestrogenic or no activity depending on the tissue and the reaction required at the time. Rather than having the same classical activity as oestrogen, phytoestrogens have many oestrogen-independent effects, such as antioxidant and anti-inflammatory properties.⁵⁰

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