Feature / Winter 2002
Chew on This!

David Jenkins and Janet Polivy both explore the power of food. 
He probes its impact on the body, while she studies its connection to the mind


David Jenkins

David Jenkins was a meat-and-potatoes boy growing up in England until one Christmas when his family tried to serve him his pet chicken.

That incident, says Jenkins, perhaps Canada’s most influential nutritional scientist, crystallized his personal ethics about food. Shortly after that, at just 13, he became a vegetarian. “I thought I might want to take another look at what I was eating,” he says with a genteel British accent that has survived 25 years in Canada. He jokes that some might call this decision “flaky,” but doesn’t apologize for it. After all, what happened that day sparked an enduring interest in food, which later evolved into a distinguished career researching the intricate processes that transform food after the first bite.

Jenkins, a professor in the Faculty of Medicine, is internationally recognized for his research on nutrition and chronic disease. He has run hundreds of dietary clinical trials at the Clinical Nutrition and Risk Factor Modification Centre at St. Michael’s Hospital in Toronto on the potential of diet to prevent and treat diabetes, heart disease and cancer. One of his most influential breakthroughs came in 1981, when he led the team that developed the glycemic index, which classifies carbohydrates according to their effect on blood-glucose levels. Jenkins and his team found that many aspects of a carbohydrate, including its physical form and the way it is cooked, determine people’s glucose response.

Today, almost any discussion about healthy eating includes some mention of fibre, but it wasn’t always so. Jenkins pioneered investigations on dietary fibre and cholesterol levels more than two decades ago. “Back in the early ’70s, if you went into the supermarket you wouldn’t have found much brown bread,” he says. “It was something you saw only in health food stores.”

In 1992, he co-wrote a study that compared the cholesterol-lowering abilities of oat bran, rich in soluble fibre, with wheat bran, rich in insoluble fibre; the results helped make oat bran a household name. More than 80 people went on low-fat diets for the study and consumed daily supplements of either oat bran or wheat bran. After two weeks, the oat bran group had significantly greater reductions in total cholesterol and harmful low-density lipoprotein (LDL) cholesterol levels than the other group. Last year, Jenkins further boosted soluble fibre’s health profile by showing that men on a diet high in soluble fibre had lower levels of prostate specific antigen (PSA) – an indicator of prostate cancer risk – than men on diets high in insoluble fibre.

Recently, Jenkins has been exploring the healing properties of another food that used to be relegated to health food stores. In 1999 he made headlines with the finding that soy foods, especially in combination with fibre, cut the risk of heart disease by lowering cholesterol. Since then, soy has become the new brown bread for the health-conscious. “The findings may explain why heart disease is so rare in East Asian countries, where soy consumption is high,” he says.

From his research Jenkins has assembled a “portfolio,” as he calls it, of dietary factors that he believes, in combination, may reduce cholesterol as effectively as some drugs. The model diet is low in saturated fat and high in soluble fibre, and includes soy protein and plant sterols, which are the plant equivalent of cholesterol.

Showcasing the portfolio is his “Garden of Eden” diet, which consists of copious amounts of fruits and vegetables, with some nuts on the side – similar to what our prehistoric ancestors would have consumed. After just one week on this diet, which contains a whopping 100 grams of daily dietary fibre (more than three times the current recommendation), plus vegetable proteins and plant sterols, participants experienced a 20-per cent reduction in their total cholesterol and a 30-per cent decrease in their LDL cholesterol levels. Jenkins joined participants and foraged caveman-style to test his thesis. “I always like to bite the bullet with the first crowd to see whether what we’re giving quite significant numbers of people is feasible,” he says. He admits the menu is not suited to 21st-century humans who don’t have time to consume 10 pounds of food daily. But eating more plant food is a good first step, he says, when obesity and diet-related ailments are becoming epidemic in the West.

Jenkins understands that the pace of modern life makes healthy eating a perpetual challenge. So, to give busy people a fighting chance at health, he often translates his research into convenient supermarket products that not only protect against disease but taste good. Last summer, Loblaws, the supermarket chain, launched a new line of soy-enriched foods based on his research.

Janet Polivy

Janet Polivy, a professor of psychology at the University of Toronto at Mississauga, is passionate about how and why people eat. After several decades of research, often in collaboration with U of T psychology professor Peter Herman, one certainty pervades her findings: weight-loss diets generally fail. “If any of these diets worked, they wouldn’t keep coming up with new ones. There would be one, it would work, and that would be what everybody used,” she says.

Over the years Polivy has made some surprising discoveries about people who continually battle the diet odds. There are real psychological differences, she says, between women who diet and women who don’t. Her studies of primarily female university students show that dieters and non-dieters in the same situations have distinct cognitive and emotional responses. In a 1994 study published in the Journal of Abnormal Psychology, Polivy put a group of dieters and non-dieters in an anxiety-producing situation. Some of the women received palatable food and some received unpalatable fare. The dieters increased their eating regardless of how the food tasted, a finding that supports other research by Polivy showing that dieters overeat when they are distressed to comfort or distract themselves or mask the true source of their stress by attributing their negative mood to overeating.

In a 1998 study, young women were told they weighed five pounds more, or less, than their real weight. The dieters who heard they were heavier reported lower self-esteem and more negative moods than the non-dieters who received the same information. These depressed dieters ate significantly more in a staged “taste test.” “It’s clear that their thinking processes are different, and this is consistent over time, so that’s why we see dieting as a personality variable, not just a behaviour restricted to eating,” says Polivy. “Dieters seem to be more conforming, more emotionally responsive and more neurotic.” Many are also susceptible to the “false-hope” syndrome, believing that losing weight will radically improve all aspects of their lives.

Specific personality traits coupled with social factors make it more likely that a woman will diet, says Polivy. “Our suspicion is that there are predisposing characteristics – one is lower self-esteem – that interact with environmental pressures. Our society, for the past 30 or 40 years, has said, ‘Fat is bad. You’ve got to be thin.'” This message also plays a key role in eating disorders, she says.

Early in her career Polivy observed what she calls the “what-the-hell effect,” where dieting leads to binge eating, a shocking finding at the time. “If you’re trying to lose weight, pigging out every time you break your diet a little bit is about the stupidest thing you can do,” she says.

At the other end of the spectrum, she has observed that people who haven’t eaten in 24 hours eat sparingly when in the presence of others who are also eating little. Her studies on the social aspects of eating show that it is the presence and behaviour of others, much more than hunger, that affect what, and how much, people eat. “Food is tremendously ritualized,” she says, and part of the ritual is that people eat like those around them.

Polivy considers diet a four-letter word – no diets are allowed at her house – but she does believe it’s important to maintain a healthy weight. And the best way to do that, she says, is to tune out the noise from the media and the diet industry and start listening to our bodies. “To eat in response to internal, not external, cues, you have to stop and think about what you’re eating and whether you’re actually hungry,” she says. She stocks her cupboards with every kind of food – including some junk food – because she is teaching her children that no food, eaten in moderation, is taboo.

“I think people waste a lot of time and energy – a lot of themselves – on dieting. Think of the productive things they could be doing with that energy.”

Megan Easton is a news services officer in the Department of Public Affairs.


Add a Comment

required, use real name
required, Not for Publication
optional, eg: BSc 2008

Next story in this issue: »
Previous story in this issue: «