Pauline Anderson

October 14, 2015

BARCELONA — Eating walnuts and cooking with canola oil may be the next hot trend in reducing risk for multiple sclerosis (MS), if results of a new study pan out.

Investigators found that individuals who consume the most foods containing plant-based polyunsaturated fatty acids (PUFAs) had the lowest MS risk. However, they found no significant association between consuming a diet high in fatty acids from fish and MS risk.

That plant-based, not fish-based, PUFAS were linked to MS came as something of a surprise, lead researcher Kjetil Bjørnevik, MD (PhD student), research fellow, University of Bergen, Norway, told Medscape Medical News.

Dr Kjetil Bjørnevik

"For the last half a century, there has been a lot of interest in PUFAs, but it has been mainly focused on fish-derived PUFAs — what we get from consuming fish. Here in our study, we don't actually see an association between those types of PUFAs and MS risk."

The study was presented here at the Congress of the European Committee for Treatment and Research in Multiple Sclerosis (ECTRIMS) 2015.

Fish Hypothesis

PUFAs are fatty acids that contain more than one double-bond in their backbone. It's believed that they have immune-modulatory, anti-inflammatory, and antioxidant properties.

Dietary intake of fatty acids has been an area of research interest in MS for several decades. Back in the 1950s, some studies suggested that people who ate lots of fish had a lower risk for MS.

Over the years, case-control studies suggested that intake of both foods rich in PUFAs (eg, fatty fish, such as tuna and salmon) and those rich in isolated PUFAS (eg, cod liver oil) was associated with lower MS risk.

A recent study showed an inverse association between MS and overall intake of the PUFA omega-3 (an anti-inflammatory α linolenic acid), particularly from fish-derived fatty acids.

"This fish-based hypothesis has been around for a long time, but now we're seeing new hypotheses, for example, some people think the lower risk is due to vitamin D intake, which is also a very hot topic," said Dr Bjørnevik.

And now another new area of interest could be PUFA-rich plants.

For the study, investigators used the large databases of the Nurses Health Study (NHS; 1984-2004) and the NHS 2 (1991–2009). Together, researchers prospectively followed 177,209 women who did not have MS at baseline, beginning in 1984 for NHS participants and 1991 for NHS 2 participants.

Using a validated food-frequency questionnaire, researchers queried all study participants about their dietary habits every 4 years. For dietary fat, they looked at intake of total fat, saturated fatty acids, and monounsaturated fatty acids as well as PUFAs. During follow-up, 479 participants were diagnosed with MS.

For all dietary fat categories, the hazard ratio (HR) for the top quintile of intake compared with the bottom quintile in both the NHS and NHS2 was below 1.0, suggesting a lowered risk for MS. The HR was lowest for PUFAs; here, higher intake was associated with a significant lower risk for MS (HR, 0.66; 95% confidence interval [CI], 0.49 - 0.90; P = .01).

This was after adjustment for age, ethnicity, latitude at age 15 years, body mass index at age 18 years, years of smoking, vitamin D supplementation, and total energy intake.

Interpret With Caution

The study results suggest PUFA intake from plants was driving the association. The MS risk for α linolenic acid was significantly lower (HR, 0.64; 95% CI, 0.47 - 0.87; P = .002) in the highest vs lowest intake groups. The HR was also lower for intake of linoleic acid in this high-intake group (HR, 0.76; 95% CI, 0.56 - 1.03; P = .04).

"We see that those people who get PUFAs from a plant-based diet, for example from vegetable oils, have a lower risk," said Dr. Bjørnevik. "This is surprising because it's not something we have seen earlier."

In addition to walnuts and canola oil, foods rich in these plant-based PUFAs include flax seeds and linseed oils, said Dr Bjørnevik. PUFAs are not found in high amounts in olive oil, which contains a different type of fatty acid, he said.

But contrary to popular belief in some circles, there was not a significant association between high intake of fish-based PUFAs and lowered MS risk in the study. The effect estimates for docosahexaenoic acid and for eicosapentaenoic acid were close to 1, indicating no association with MS risk.

Results of an analyses using the cumulative average intake of PUFAs during follow-up were similar.

It's impossible to determine from this study how much plant-based PUFAs one needs to consume to lower MS risk. "We just saw that those who ate the most had the lowest risk," said Dr. Bjørnevik. "It's one of the first studies showing this so it's hard to quantify a specific amount."

He emphasized that because this is the first study uncovering this association, "you have to interpret it with caution and it needs to be replicated."

As well, he said, experts can't determine from the study whether plant-based PUFA intake has any benefits, for example disease-modifying effects, on the course of the disease. "It's an interesting finding, but it's very preliminary."

Session co-chair Gilles Edan, MD, professor, clinical neurology and chair, Department of Neurosciences, University Hospital of Rennes, France, said that although he's not a PUFA expert, he found Dr. Bjørnevik's presentation "clear and rather convincing" and that the study was "well designed."

However, examining in detail the quality of scientific data will have to wait until the study is published in a peer-reviewed journal, he said.

Dr Bjørnevik and Dr. Edan have disclosed no relevant financial relationships.

Congress of the European Committee for Treatment and Research in Multiple Sclerosis (ECTRIMS) 2015. Parallel Session 7, #168. Presented October 9, 2015.

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