Plant-based Diets for Human Health with Vasanti Malik, ScD, Research Scientist

I recently attended a conference at the Culinary Institute of America with the Peanut Institute. Harvard scientist Vasanti Malik spoke on plant-based diets on health. Here is the transcript of her presentation.

In recent decades, there is an increased prevalence of obesity. For the first time, in 2008, the world had more people that were overweight than underweight. The prevalence in 1980 was just under 8% of women who were obese, and it doubled in 2008. There was a similar increase in men. Obesity is a pipeline for disease, obesity and diabetes travel together. There is a steady rise in obesity in all parts of the world over time, from low-income to high-income countries. The U.S. was the epicenter of diabetes, but now it’s a global problem. The prevalence is creeping up; the number of people with diabetes in the US is 30 million. This is expensive; many countries are spending over $5 billion per year. In the top 10 cases of death in 2013 in the U.S. (heart disease is number 1), diet is the number one associated risk factors. Diet is modifiable.

In the 1960s, the researcher Ancel Keys launched the Seven Countries Study, and he found that countries that consumed the most saturated fat had the greatest incidence of coronary heart disease. Consuming a more animal-based diet was linked with the highest risk, compared to mostly plant-based diets with the lowest risk.

Not all studies are created equal. Ecologic, cross-sectional, and case-control studies are not the best studies to look at diet and health. When you look at the relationship with diet and disease, you want to look at it over time. A lot of our work is on cohort studies, we look at people over time. The gold standard is randomized control trials, which are randomized to an intervention diet and control diet. You can balance out risk factors, such as smoking. You are getting rid of the issue of confounding—we worry about this in observational studies. The tricky thing with trials is that it’s not always feasible with diet and disease to look at diet for a long period of time. Participants wouldn’t comply.  Meta-analyses use a statistical approach using results from numerous studies, and combine them to give you an overall average. More and more guidelines are based on these.

A lot of research that I’m sharing with you is based on our Harvard cohorts: Nurses’ Health Study, Nurse’s Health Study II, Health Professionals Follow-Up Study.

In an older study by Dariush Mozaffarian, the relationships between changes in food and beverage consumption and weight changes were investigated every 4 years, looking at dietary factors. The average person gains one pound per year, and thy found that some dietary factors are linked with less weight gain over time. Processed meat and unprocessed meats popped up as an increased risk of weight gain. The Western world is where meat consumption is happening—in 2012, we were coming 100-130 kg per person in U.S., which is among the highest in consumption. Meat intake us rising in low-income countries, too. If you look at meat consumption per capita, it is rising in Brazil, China, India, and South Africa.

Our studies have shown that red and processed meat are linked to increased risk of diabetes, coronary heart disease, stroke, and certain cancers. We have done substitution models. We asked, what would happen if you replaced one serving of red meat per day with another option? We replaced one serving per day of red meat with other foods. With one serving of nuts per day you could reduce the risk of type 2 diabetes by almost 23% diabetes. We did a similar modeling for heart disease, and replaced one serving per day with other protein sources, and we found decreased risk of coronary heart disease—we found when we replaced red meat with poultry, fish, nuts, and beans a 20-40% benefit. There was a similar substitution analysis for total mortality. In the Harvard cohorts, when we replaced red meat with nuts we found a reduced risk of 20%.

In a meta-analysis of the relationship between nut consumption and risk of type 2 diabetes and cardiovascular disease mortality, the greatest amount of nuts was linked with the lowest risk of diabetes—16% reduced risk. This is due to the improvement in body weight. The same benefit for more nuts was seen with cardiovascular disease—six servings per week it went down by 30%, and for mortality six servings per week it went down by 15%. The evidence base is out there.

In a substitution analysis, plant protein vs. animal protein and the substitution of peanuts and peanut butter reduced the risk of diabetes—substituting it for processed meat once per day reduced risk by 20%.

We looked at different types of nuts and mortality in the Nurses’ Healthy Study and Health Professionals Follow-up Study in a pooled cohort. For those that consumed peanuts two or more times per week vs. never consuming them, had a just under 12% reduced risk of all cause mortality. For heart disease mortality, there was a reduced risk of 25%. This is great news, because peanuts are not expensive and good for all these populations.

Why are peanuts beneficial? They are rich in beneficial dietary fiber, plant proteins, healthy fats, micronutrients, phytochemicals, and arginine—an amino acid, which we are interested in regarding how it confers benefits. Peanuts are a holistic food, with a number of health benefits.

We know that eating red and processed meat is unhealthy, so if we replaced it with healthy sources of protein it is beneficial. But what is a plant-based diet? There isn’t a universal definition of what it means. It’s difficult to study. We are not going to tell people to become vegetarian, but we know that some plant-based foods aren’t healthy. We came up with a graded approach—a spectrum of what is a proportion of plant-based foods related to animal foods. We did this in our cohort, and compared plant-food groups that are healthy, including whole grains fruits, vegetables, nuts, legumes, vegetable oils, tea and coffee with less healthy plant foods, such as fruit juice, refined grains, potatoes, sugar sweetened beverages, sweets and desserts.

My colleague did an analysis looking at healthy plant-based foods compared with less healthy plant-based foods and animal foods and found that healthy plant-based foods are associated with lower risk heart disease, and animal and less healthy plant foods were associated with greater risk of heart disease. Plant-based foods reduced the risk when all of these were combined, but unhealthy plant based foods increased the risk. We saw that people who consumed 20 servings of healthy plant-based foods found the greatest benefit—doubling the effect of the benefit seen for 5-6 servings per day. We have seen this effect in diabetes, heart disease, and weight change—they are also studying this in cancer.

In the Dietary Guidelines 2015, the scientific advisory committee recommended a plant-based diet for health and even for sustainability, but that part didn’t make it into the actual Dietary Guidelines. The way it works is that the scientific advisory committee comes together and goes over the evidence and puts together the recommendations that go to Congress, and the Dietary Guidelines comes out. What is recommended doesn’t always make it through. Maybe we will see it in 2020. The fact that it was on the agenda is interesting.

Why was planetary health in the Dietary Guidelines? One reason is climate change—it is happening and we need to try to mitigate its impact. Scientific communities are trying to come up with strategies, such as reducing animal products. Animal-based foods are harder on the environment in terms of land use, they use more fresh water and increase greenhouse gas emissions, compared to plant-based foods. In a comparison of greenhouse gas emissions from various food types, peanut butter and peanuts, have quite a lower impact compared to animal foods. Compared to a hamburger, a PB&J could save 3.5 pounds on carbon dioxide emissions, 280 gallons of water, and 12 – 50 square feet of land from deforestation or overgrazing. Hopefully it’s on whole wheat bread. In a comparison of other nuts, some more than others, it takes over 20 times more water to produce ounce of almonds compared to peanuts, which also have nitrogen fixation benefits.

There are huge implications for U.S. and high-income countries, as well as low- and middle-income countries. It’s a source of protein that doesn’t require as much water, which is important. It is beneficial for addressing undernutrition, and the double burden of disease; in Africa there is diabetes and cardiovascular disease while there is still undernutrition and deficiencies. Peanuts can be grown locally. They are grown typically in Africa by women, which can empower women. They are culturally acceptable, so we don’t have to try encouraging a new product.

In the Sustainable Development Goals 2015, 190 world leaders committed to 17 goals to reduce poverty, inequality, injustice, and climate change related to nutrition and sustainability. The World in 2050 goal is that by 2050, we can provide a global population of nearly 10 billion a healthy and sustainable diet. We have nearly 1 billion undernourished people in the world and 2 billion are obese, and we are not meeting the Paris Climate Agreement for global warming. Animal-based foods are associate with weight gain, increased risks of disease, and they are less environmentally sustainable. The benefits of plant-based foods, such as nuts and peanuts, are clear.

Image: Thai Tempeh Noodle Skillet, Sharon Palmer, RDN