October 2016 Issue
Low-Fat Vegan Diets
By Sharon Palmer, RDN
Vol. 18, No. 10, P. 20
Today's Dietitian speaks with experts and explores the science concerning this popular plant-based eating pattern.
The "whole foods, plant-based diet," a low-fat vegan diet focusing on whole plant foods, is gaining traction.
Thanks to the popularity of the movies Forks Over Knives and PlantPure Nation (and accompanying campaigns), the book The Engine 2 Diet: The Texas Firefighter's 28-Day Save-Your-Life Plan That Lowers Cholesterol and Burns Away the Pounds, and the works of doctors Caldwell Esselstyn, Neal Barnard, Dean Ornish, and T. Colin Campbell (among many others), a culture of plant-based eating is growing in popularity. All of these experts present varying views on a central theme: The optimal diet focuses on whole plant foods, such as pulses, whole grains, nuts, seeds, fruits, and vegetables, and eliminates animal foods and processed foods, including refined oils, sugars, and grains—essentially a low-fat vegan diet. This overall diet, which has taken on the term "whole foods, plant-based diet," can be seen at Whole Foods Market, which promotes The Engine 2 Diet's "Plant Strong" foods and products; at plant-based nutrition conferences for health care professionals, in films, on cruises, and in the news as celebrities proclaim the diet's benefits.
In this article, Today's Dietitian asks top plant-based nutrition experts to weigh in on the science behind the diet.
"I have definitely seen an increase in the number of clients and consumers interested and participating in, adapting to, and mastering this approach to eating," says plant-based nutrition expert Julieanna Hever, MS, RD, CPT, author of Plant-Based Diets: A Physician's Guide. Matt Ruscigno, MPH, RD, past chair of the Vegetarian Nutrition Dietetic Practice Group and coauthor of No Meat Athlete, credits the popularity of the film Forks Over Knives to the popularity of the diet, noting that followers of the diet are "very passionate."
Are dietitians in tune with the movement? "I think RDs are becoming more educated about the health benefits of low-fat, plant-based diets and the risks associated with consuming high levels of animal products," says Karen Smith, RD, senior dietitian at Physician's Committee for Responsible Medicine, an organization led by Barnard. "However, there are still many RDs who have little to no knowledge of these diets, and this pattern of eating isn't taught to dietetics students as an intervention for preventing and reversing disease processes," Smith says. "There does appear to be a general trend among the majority of RDs to educate clients on the importance and health benefits of incorporating more plant foods into their diets."
A couple of decades ago, vegan diets often were considered risky among the health profession community, but today a growing number of studies have shown health benefits linked with vegan diets, which have less saturated fat and cholesterol and more fiber, folic acid, vitamins C and E, potassium, magnesium, and phytochemicals than nonvegetarian diets. Vegans tend to be thinner, have lower serum cholesterol, lower blood pressure, and reduced risk of cardiovascular disease.1 Data from the Adventist Health Study-2 (AHS-2) found that vegan diets confer extra protection beyond lacto-ovo vegetarian diets against obesity, hypertension, type 2 diabetes, and cardiovascular mortality.2
While there may be a growing understanding that well-planned vegan diets are healthful, what about the benefits of low-fat, whole foods, plant-based diets? What's not to love about a diet that focuses on real, whole plant foods, maximizing nutrition in every bite while eliminating low-nutrient calories? Indeed, some research links this diet to reversal of heart disease and improvements in blood glucose among people with diabetes. But it gets a bit more complicated than that. A wide variety of opinions exist among plant-based dietitian experts. Some believe there are convincing benefits behind this diet, while others believe more research is needed.
Heart Health and Diabetes Treatment
Brenda Davis, RD, a plant-based expert and coauthor of Becoming Vegan, says that researchers have clearly demonstrated that by reducing calories from fat to no more than 10% and dramatically reducing harmful fats, heart disease can be successfully treated (and in many cases reversed), and type 2 diabetes can be effectively treated.
Esselstyn published a study, which included 22 patients with severe coronary artery disease who took cholesterol-lowering drugs and followed a very low-fat diet (no more than 10% of calories). Of the 22 participants, five dropped out and 17 maintained the diet, 11 of whom completed a mean of 5.5 years of follow-up. All of the 11 reduced their cholesterol levels from a mean of 246 mg/dL to below 150 mg/dL. Lesion analysis by percent stenosis showed that of 25 lesions, 11 regressed and 14 remained stable. Mean arterial stenosis decreased from 53.4% to 46.2%. Disease was clinically arrested in all 11 participants, and none had new infarctions. After 10 years, six continued the diet and had no further coronary events, whereas the five dropouts resumed their prestudy diet and reported 10 coronary events.3
In a study led by Barnard, which included 99 people with type 2 diabetes, participants ate either a low-fat vegan diet or the standard American Diabetes Association (ADA) diet. After 22 weeks, 43% of the vegan group and 26% of the ADA group reduced diabetes medications, and the HbA1c for the vegan group decreased by 0.96 percentage points and 0.56 percentage points for the ADA group.4
Ornish has published studies demonstrating that his lifestyle plan, including a 10% fat whole foods vegetarian diet, helped reverse prostate cancer, heart disease, and diabetes. The Lifestyle Heart Trial—a randomized controlled trial with 48 patients with moderate to severe coronary heart disease—investigated whether patients could be motivated to make and sustain Ornish's lifestyle plan and if it would stop the progression of coronary atherosclerosis without lipid-lowering drugs. After one year, the participants on the lifestyle program had a 37% lowering of LDL cholesterol and 91% reduction in frequency of angina. Average percent diameter stenosis regressed from 40% to 37.8%, compared with the usual-care control group who had a 165% increase in angina and progressed from 42.7% to 46.1% in percent diameter stenosis. When the study was extended four years, even greater regression of coronary atherosclerosis was found, compared with the control group, which had more than twice as many cardiac events.5 It's important to note that diet was just one component of the lifestyle plan.
While these findings are impressive, there are a few considerations plant-based experts raise. Davis says that we can't assume that because very low-fat diets help to reverse heart disease that such diets set the gold standard for everyone eating plant-based diets. And plant-based expert Reed Mangels, PhD, RD, nutrition adviser of The Vegetarian Resource Group, says she hasn't seen a direct comparison of a low-fat, plant-based diet with a higher-fat, plant-based diet in terms of health effects.
"Given what we know about the benefits of plant foods that are rich in healthful fats, it's reasonable to expect that higher-fat, plant-based diets would be just as beneficial and perhaps have even more benefits," says Virginia Messina, MPH, RD, vegan expert and coauthor of Vegan for Life. A Czech Republic study found benefits for people with diabetes who followed a high-fat (38%) almost-vegan diet.6 Messina also highlights that Esselstyn's study didn't include a control group or look at effects of weight loss and other potentially confounding variables, making it difficult to draw conclusions about the true effects of fat restriction. "We just don't have the data to suggest that restricting dietary fat intake is necessary for good health and for treating disease. It's much more likely that building a diet around healthful plant foods and choosing healthful fats is important," Messina adds.
However, Smith offers a different viewpoint. "Atherosclerosis does not occur overnight. It takes years for plaque to build up in artery walls before problems arise. Therefore, a low-fat, plant-based diet is not only beneficial for people already diagnosed with heart disease, but can prevent it from occurring in the first place."
How Much Fat Is Optimal?
Within a vegan diet, what's the ideal amount of fat? According to plant-based expert and founder of Kailo Nutrition, Heather Borders, MBA, RD, LD/N, when one focuses on consuming a variety of unprocessed plant foods, the percentage of calories from fat is typically going to land around 10% to 15% of total calories—this is the level recommended by many whole foods, plant-based diet plans. This is in contrast with the Acceptable Macronutrient Distribution Range (AMDR) from the Dietary Reference Intakes, which recommend adults consume 20% to 35% of total calories from fat, with higher levels for children and adolescents.7
Border stresses that a whole foods, plant-based diet focuses on low fat, not no fat. "There is also an emphasis on whole foods vs refined foods. In the plant kingdom, nuts, seeds, avocados, and olives are whole, unprocessed sources of fat, including the essential fatty acids. They also happen to be packaged with fiber, vitamins, and minerals."
"I think that most adults can probably enjoy good health on very low-fat diets, but it does take more attention to detail to ensure adequate intake of nutrients," Messina says.
While Mangels believes that the use of the AMDR hasn't been studied extensively in populations eating a plant-based diet, she thinks a plant-based diet within this range of fat could be health promoting, provided that energy and nutrient needs are met. She also cites data that shows vegan men who ate 30% of calories as fat had average cholesterol levels of 158 mg/dL, supporting the benefits of more moderate fat intake.8
Two cohorts (EPIC-Oxford in the United Kingdom and AHS-2 in North America) of similar, health conscious individuals with different dietary patterns, including meat eaters, semivegetarians, fish eaters, lacto-ovo vegetarians, and vegans may shed some light, Davis says. "The fat intake of the vegetarians and vegans within these cohorts is in the range of the AMDR, and these groups have significantly lower rates of mortality and chronic disease compared with the similar, health conscious nonvegetarians," Davis says. Fat intakes within Blue Zone populations (a demographic where people live longer) range from about 10% of total calories from fat in traditional Okinawan diets to about 35% of total calories from fat in the Mediterranean diets of Ikaria, Greece, and Sardinia, Italy, she adds.
Eliminating or severely restricting high-fat plant foods can put some individuals at a disadvantage, according to Davis. She recommends a lower limit of 15% of calories from fat for healthy vegan adults, with higher intakes for children, pregnant and lactating women, and athletes. Davis lists potential disadvantages of very low-fat diets (≤10% fat) such as insufficient essential fatty acids (particularly omega-3 fatty acids); reduced absorption of fat-soluble phytochemicals and vitamins A, D, E, and K; increased triglyceride levels (when carbohydrates are refined, though this can be averted with whole plant foods), reduced HDL cholesterol, increased production of small dense LDL cholesterol (the type more readily incorporated into arterial plaque), insufficient energy (particularly for infants, children, and some adults with high energy needs), and reduced intake of nutrients and other protective dietary components.
One of the most crucial lessons may be to think beyond a one-size-fits-all approach. "Optimal fat intakes must support excellent health at every stage of the life cycle, including periods of rapid growth and development, such as pregnancy, infancy, and childhood," Davis says. Mangels adds that she's especially concerned about the effects of very low-fat diets on healthy children.
Type of fat rather than amount may be what really matters, Messina says. When dietary fat comes predominantly from minimally processed plant foods, excellent health can be maintained even when fat intake is relatively high, Davis says, adding, "The one thing experts agree on is that it is not high-fat whole foods such as nuts, seeds, avocados, or olives that are responsible for the epidemic of chronic disease that plagues us."
Avoiding Refined Oils
Another controversy surrounding low-fat, plant-based diets includes recommendations to avoid refined plant oils. Hever notes that because oil is the most calorically dense food available, omitting it is one of the easiest ways to dramatically reduce calorie intake and support a healthy weight. "Since there are other lower-calorie, more nutrient-dense options for attaining the fats found in plant oils, reducing oil intake is a wonderfully useful tool to help my clients achieve their goals," says Hever, who emphasizes fats from whole food sources. Smith notes that in the standard American diet, refined oils are used heavily, and the calories they provide quickly add up and can be a contributor to weight gain and obesity.
Borders emphasizes that all oils are 100% fat, with varying levels of saturated fat. Olive oil is about 14% saturated fat, and tropical oils are more than 80%. "There's no fiber or minerals, and with 120 calories per tablespoon it's incredibly easy to consume more calories than intended. Calorie for calorie, oils are just not nutrient-dense. Also, oils aren't satiating; individuals will still end up eating the same amount of food calories throughout the day. Filling up on whole food forms of fat will provide more nutrients and health benefits than refined and processed forms of fat," Borders says.
"While it's well accepted that humans require some dietary fat, there's no requirement that the source of that fat be vegetable oil," Mangels says. She notes that some individuals may find it easier to lose weight by eliminating oils, but in other cases the addition of some oil can help with weight maintenance or growth, especially in cases where energy needs are high and it's challenging to meet those needs on high-fiber, plant-based diets, including young children, pregnant women, and some athletes.
Messina believes that while vegetable oils certainly aren't required in diets, it doesn't mean that small amounts are unhealthful or that they can't be included in heart-healthy diets. She points to the use of these oils in traditional diets with low rates of heart disease, such as the Mediterranean and Okinawan diets.
While Davis agrees with the value in minimizing intake of oils, particularly for overweight individuals suffering from chronic disease, she notes that high-quality oils can be a part of a healthful diet if used judiciously. "They can make meals more enjoyable, add extra calories without adding bulk, and help improve the absorption of fat-soluble vitamins and protective phytochemicals. The higher the energy needs of the individual, the more wiggle room they have," Davis says.
Molly Hembree, RDN, LD, a plant-based expert and retail dietitian at The Little Clinic of Kroger, says, "When aiming for a whole foods-based approach, added oils will naturally be sparser. The polyunsaturated fats from omega-3 and omega-6 fatty acids are essential and must be included, and these are oftentimes in vegetable oils, so it would be wise to include at least a minimal amount."
In addition, many supporters of the whole foods, plant-based diet point to evidence showing adverse effects of oils on endothelial function. "Studies show refined oils result in stiffening of arteries, damage to the endothelial lining, and subsequently less nitric oxide production," Borders says. A scientific review found that endothelial function is adversely affected with a high-fat diet, and that olive oil had the same impairment to endothelial function.9 A more recent study of 10 participants consuming soups with 60 mL (four tablespoons) of one of three oils (olive, soybean, and palm) found all of the oils produced similar acute adverse effects on endothelial function and postprandial increases in triglyceride levels.10
However, Messina reports that research suggesting vegetable oils have acute detrimental effects typically used single, unhealthful meals that are extremely high in fat. "The findings are not relevant to those consuming smaller amounts of vegetable oils as part of a diet that's built around whole plant foods and that's rich in phytochemicals including antioxidants." In addition, many other studies have found beneficial effects of moderate intakes of plant oils. In a systematic review and meta-analysis, evidence supported olive oil's beneficial effects on endothelial function and markers of inflammation.11
While opinions vary over the benefits of a plant-based diet, one thing seems clear: Dietitians have an increasing role to play in promoting optimal health through increased intake of whole plant foods. Staying on top of the science and trends is paramount.
— Sharon Palmer, RDN, is a plant-based food and nutrition expert, author of Plant-Powered for Life, and nutrition editor of Today's Dietitian.
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