The perils of protein

Report from the ‘Paleo vs Plant Based? Tackling Current Controversies in Nutrition’ seminar – Part 1

Last Wednesday I attended the ‘Paleo vs Plant Based? Tackling Current Controversies in Nutrition’ seminar at Sydney Adventist Hospital, featuring the renowned Canadian dietitian and author Brenda Davis; the grande dame of the Australian nutrition scene, Rosemary Stanton; and diabetes and PCOS expert, Kate Marsh.

The packed auditorium, and the organisers’ announcement that the event had been sold out, with a recording to be made available to those who missed out on tickets, were powerful indicators that the conflict between the Paleo and plant-based dietary movements is the hottest topic in nutrition right now.

Over the next 3 editions of EMPOWERED!, I’ll be summarising each of the lectures for you, to help you be a more informed consumer of all the confusing, contradictory health information that comes your way each day through the news media and Internet.

Lecture 1: Plant-based Diets and Chronic Disease

Kate Marsh kicked off the seminar with a summary of the research that has been carried out on plant-based diets and health. Broadly speaking, there are 2 major types of study design in nutrition research:

• Observational studies, which analyse the customary eating habits of a large group of subjects over a long period of time, and then look for correlations between those habits and the subjects’ health outcomes; and
• Intervention studies, in which subjects are instructed to change their diet in a particular way, and the effect of this change on their health is examined.

I’ve discussed the 2 primary observational studies – the Adventist Health Study-2 and the EPIC (European Prospective Investigation into Cancer and Nutrition) study – that have established the benefits of plant-based eating, in my previous article Eating Meat: The Fast Track to Diabesity.

Focusing on the intervention studies, Kate summarised the findings of Dr Neal Barnard and his team, which I covered in my International PBNHC Round-Up Webinar. Compared to the omnivorous diet recommended by the American Diabetes Association, a low-fat wholefood plant-based diet:

• Reduced HbA1c (a marker of blood sugar control) by over 3 times as much as those on the ADA diet;
• Reduced LDL cholesterol by more than twice as much;
• Resulted in more than twice as much weight loss; and
• Allowed those on the plant-based diet to reduce their medication usage by 43% compared to only 26% in the ADA group.

She also discussed the weight loss trial conducted by Gabrielle Turner-McGrievy, which randomised 50 overweight adults to one of 5 different versions of a low-fat, low-glycemic index diet, for 6 months:

1. Vegan,
2. Vegetarian (including dairy products and eggs but no flesh foods),
3. Pesco-vegetarian (including dairy products, eggs and fish but no flesh foods from land animals),
4. Semi-vegetarian (eating flesh foods less than once per week), or
5. Omnivorous (eating all animal products regularly).

None of the prescribed diets emphasised restriction of calories, but despite this participants in all 5 groups lost weight. However, those assigned to the vegan group lost more than twice as much weight as those assigned to the pesco-vegetarian, semi-vegetarian and omnivorous groups, losing on average 7.5% of their body weight in 6 months.

Advocates of the Paleo diet would argue that their high protein, restricted carbohydrate plan cannot be compared to a regular omnivorous diet. True enough. It’s much worse. When Wendy Russell and her colleagues studied what happened to the gut bacteria of people who went on high-protein, low-carbohydrate diets, they found something truly frightening.

Firstly, their study subjects – 17 obese men – were put on a ‘normal’ diet containing 85 g protein, 116 g fat, and 360 g carbohydrate per day for 7 days, in order to get a baseline measure (through analysis of stool samples) of their gut bacteria and the ‘metabolites’, or biologically active molecules, that they produce. These metabolites exert a powerful influence on the health of the human colon, and in particular the risk of colorectal cancer.

Then the men were put on either a high protein, moderate carbohydrate diet (139 g protein, 82 g fat, and 181 g carbohydrate per day) or a high protein, low carbohydrate diet (137 g protein, 143 g fat, and 22 g carbohydrate per day) for 4 weeks. At the end of the 4 weeks they were switched to the other diet, so that all the men tried both versions of the high-protein diet.

Both versions of the high-protein diet resulted in higher concentrations in the stool of compounds associated with an increased risk of colonic disease: branched-chain fatty acids, phenylacetic acid and N-nitroso compounds.

In addition, the low-carbohydrate version of the high-protein diet decreased the proportion of the beneficial fecal short-chain fatty acid butyrate, which protects against bowel cancer, along with phenolic acids which act as powerful antioxidants. These harmful changes were associated with reduced numbers of Roseburia/Eubacterium rectale bacteria.

The researchers warned that, since they had measured such dramatic changes in gut bacteria and metabolites after just 4 weeks on high protein diets,

“Long-term adherence to such diets may increase risk of colonic disease.”

This was not a one-off finding; in 2009 another team of researchers found that a very low carbohydrate diet reduced stool size and frequency, concentrations of short chain fatty acids, especially butyrate, and counts of the highly beneficial bifidobacteria.

In contrast, according to a detailed review by Marian Glick-Bauer and Ming-Chin Yeh, vegans harbour gut bacteria that protect against

• Intestinal disorders;
• Inflammation;
• Obesity;
• Type 2 diabetes;
• Cardiovascular disease;
• Colon cancer; and
• Autoimmune disease

While the absence of animal products exerts a significant influence on the gut bacteria of vegans, the presence of dietary fibre – found only in whole plant foods – is just as important. Fibre doesn’t just make your bowel movements larger and easier to pass; it also stops pathogenic bacteria from adhering to the bowel wall, favourably alters bacterial fermentation patterns and short chain fatty acid concentrations, and changes the composition of your gut bacteria population.

Of course, not all vegans eat the kind of diet that encourages a healthy gut microbiota, so not all vegans are slim, healthy and enjoying protection against chronic disease! Dietary fibre, and its close cousin, resistant starch, are both necessary for beneficial gut bacteria to thrive, and a diet of highly processed vegan ‘junk food’ is just as deficient in these crucial components as a regular omnivorous diet.

Need help with planning an optimally healthy plant-based diet? Have some burning questions on nutrition that you just haven’t been able to get reliable answers to? Become an EmpowerEd member today!