Business & Policy
Controlling weight gain with potatoes?
By Carolyn King
A potato extract that’s rich in beneficial compounds is looking very promising. In trials with mice, researchers at McGill University have found that this extract reduces weight gain and provides other important health benefits. Now, they hope to conduct clinical trials to see if the extract produces similar benefits in people.
In this research, Danielle Donnelly, a potato researcher in McGill’s department of plant science, has teamed up with Stan Kubow and Luis Agellon, who are both at McGill’s school of dietetics and human nutrition. The research had its beginnings in Donnelly’s research on genetic improvement of Russet Burbank, the number one processing cultivar in Canada.
Because Russet Burbank has limited fertility, traditional breeding techniques aren’t effective for developing improved lines. So, about 10 years ago, Donnelly and her research group developed a technique using tuber tissue to propagate plantlets that can differ genetically from the original tuber. These variants, called somaclones, can then be grown in the field and screened for various traits. Donnelly has produced about 800 Russet Burbank somaclones.
“I had been screening my somaclones of Russet Burbank for yield and processing characteristics after long-term storage, and doing the selections and realizing that the somaclone technology could be very helpful there,” Donnelly explains. “Then, in talking to Stan Kubow, I realized that we should also be looking at nutritional parameters because the processing industry, and the whole potato industry, needs to be more concerned about the health of their consumers.”
Donnelly and Kubow started collaborating on potato nutrient research. In one part of this research, they examined the mineral content of 16 cultivars, including chippers, fryers and table stock, grown at five locations. “We found there was a lot of variation between the cultivars. Potatoes are not created equal for minerals! Russet Burbank and Yukon Gold were particularly good,” Donnelly says.
They determined that one serving per day of Russet Burbank, Yukon Gold or Freedom potatoes provides a significant portion of the recommended daily intake for magnesium, phosphorus, potassium, copper, iron, selenium and zinc.
In another part of their nutritional studies, Donnelly and Kubow determined the antioxidant levels in her top 25 somaclones that were best for yield and processing traits. In potatoes, antioxidant activity comes from vitamin C, a number of polyphenolics and other compounds. Out of the 25 somaclones, they selected the four that had the highest antioxidant activity plus a range of polyphenolic compounds.
From this screening and selection work, Donnelly currently has four advanced lines moving toward registration. She hopes to register the best one or two of those lines later this year. “All four lines have high yield, three of them do better than the Russet Burbank control in fry tests, and all have very high protein and high antioxidant capacity,” she notes.
In a different aspect of the potato nutrient research, Agellon, Kubow and Donnelly investigated the effects of potato polyphenols on diet-induced obesity. The possibility that eating polyphenols might control obesity may seem surprising, but obesity actually has a connection with inflammation. Research has shown that obesity results in low-grade chronic inflammation due to the reaction of certain cells to excess nutrients and energy.
As a first step, Kubow and Donnelly grew 12 different potato cultivars for several growing seasons and compared their polyphenolic contents. They found that Onaway and Russet Burbank had higher and more consistent polyphenol levels than the other cultivars.
Next, using these two cultivars, the researchers made an extract containing a mixture of potato polyphenols. “The extract concentrates the active ingredients, making it more likely to see the biological effects we were interested in,” Kubow explains. One dose of the extract has about 30 times the amount of polyphenols found in a single potato. The main polyphenol in the extract is chlorogenic acid, which has been shown to have anti-obesity effects in some situations.
Then the researchers conducted a feeding trial with mice to evaluate the effect of the extract. “The mice were fed a diet that is similar to what many North Americans consume; it is high in calories, high in fat, and high in sugar content. We wanted to see if these polyphenols, when given to mice that are ingesting this high-fat diet, would help in preventing obesity,” Agellon says.
One group of mice was fed just the high-fat diet. A second group was fed the high-fat diet plus the potato extract. And a third group was fed the high-fat diet plus an equivalent amount of a purified single polyphenol, either chlorogenic acid or ferulic acid.
“We were intrigued by a number of studies that tested single polyphenols reported to be active in some systems but that were not as effective when used in a purified form; it seems that the purified compound had lost its potency,” Agellon explains. “We wondered if the desirable effect associated with a food like potato and the polyphenols that it contains, is because of a combination of the different compounds in the food.”
Their hypothesis was that each individual polyphenolic compound produces a small benefit for a particular area of the body, like the liver, but multiple polyphenols ingested together affect multiple pathways, producing a synergistic effect with major health benefits.
Agellon says the extract’s benefits emerged quite quickly in the trial. “Midway through the 10-week study, we could see which of the groups had received the polyphenol extract. They had less weight gain and were much more active than the mice receiving the high-fat diet by itself.”
Kubow adds, “This effect wasn’t because the mice didn’t like the diet and didn’t eat it. They were eating as much or more of the high-fat diet [as the other groups of mice]. Normally, mice respond just like humans – if they eat a lot of fat, they gain a lot of body fat and body weight. But to our surprise, the extract had quite remarkable potency in inhibiting that, regardless of how much they ate.”
The individual polyphenols were not quite as effective as the extract in reducing weight gain, suggesting synergistic benefits from the mix of polyphenols in the extract.
The researchers are excited by the extract’s potential human health benefits. Agellon notes, “The extract could be a wonderful tool to help people suffering from obesity.” To move forward on this, they need to conduct clinical trials to assess the extract’s fat-fighting effect in people. “We’ve got a lot of data supporting this effect in animal trials and in some culture trials, but clinical trials are the key, critical step toward commercialization,” Kubow says.
The researchers have also looked at the extract’s effect on another inflammation-related health problem: lung damage caused by air pollution. Kubow explains, “Inflammation is your immune system overreacting to various compounds, including pollutants. With air pollution, that overreaction causes damage in various tissues including the lungs. So our hypothesis was that the extract might be effective where people are overweight and exposed to pollutants at the same time.”
In this study, they fed two groups of mice a western-style diet, similar to the diet in the obesity trial but not quite as high-fat. For four weeks, one group was fed the high-fat diet, and the other group was fed the high-fat diet plus the extract. Then the mice were exposed to ozone for four hours, to replicate the effects of exposure to heavy smog. “We looked at their lungs 24 hours after that exposure because the body is continually overreacting with the inflammatory response. That allowed us to detect factors in the lungs associated with ozone damage and inflammation,” Kubow explains.
The results showed that the mice eating the potato extract had significantly less lung damage. “We think this study was an important first step to validate the use of this extract as a means of potentially having a supplement to combat air pollution, which would be the first such supplement,” Kubow says. “However, we need clinical trials for verification of the benefit in humans.”
Clinical trials are key
The researchers are currently seeking funding for clinical trials to see how well the extract fights obesity and lung damage in people. If those trials prove the extract’s effectiveness, then the extract could have commercial potential, for instance, as a dietary supplement or a cooking ingredient. So investment in the trials could be of interest not only to health agencies but also to the potato industry because of the extract’s value-added potential.
Donnelly sees a couple of ways the next steps in this research could help potato growers and processors. “First, there are the clinical trials, which would get a product out there. Secondly [with information on polyphenol levels in more cultivars] it could be that more potato growers could benefit because there is a lot of wasted potatoes – people growing small potatoes have big ones they can’t use, and big potato growers have little ones they don’t always know what to do with. It may be that some of these materials could be rescued from waste streams from processed potatoes. So there is a lot of potato that could be used for a product that no one has produced up until now, which is this extract.”
As well, a potato extract with proven health benefits might help enhance the health reputation of potatoes. Kubow says, “The public perception is that potato intake is bad for your weight, but we’re talking about potato decreasing the risk of overweight and obesity.”