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The #1 Reason Why You're Not Losing Weight

For vegans frustrated by weight gain instead of loss, scientists may have an easy fix.

You'd think that adopting a vegan diet would offer a quick and healthy route to weight loss. After all, the vegan diet is entirely plant-based, which nutritionists say is great for maintaining a healthy weight. However, according to a new study out of the German Federal Institute for Risk Assessment, it turns out a vegan diet can inadvertently lead to weight gain.

The reason? The vegan diet offers little in the way of iodine, a mineral essential to thyroid function. Thyroid function is critical to keeping the metabolism running efficiently. Thyroid dysfunction, aka hypothyroidism, is associated with weight gain.  (Related: 21 Best Healthy Cooking Hacks of All Time.)

Scientists at the Institute wanted to compare vegan and non-vegan diets in terms of how well each supplies essential vitamins and minerals, including iodine. The body does not manufacture iodine, according to the American Thyroid Association. That means maintaining adequate levels is dependent on diet (or supplementation). Unfortunately for vegans, dietary sources of iodine are largely animal-based (the exceptions are seaweed, soy, and iodized salt).

Led by Dr. Cornelia Weikert, MPH, the research team recruited 72 non-obese adults comprising 36 men and 36 women between the ages of 30 and 60, half of whom were vegan (18 men and 18 women). Each filled out a questionnaire regarding their demographics and supplement-use. Each had their height, weight, and other vitals measured at the outset of the study. And each kept a record of what they consumed over a three-day period.

At the end of that period, the participants provided blood and urine samples for nutrient analysis. What that analysis revealed is that the vegans had significantly higher levels of dietary fiber, vitamins E and K, folate, and iron, but significantly lower levels of iodine, than non-vegans. In fact, one-third of the vegans were iodine-deficient, based on thresholds set by the World Health Organization.

No significant difference between vegans and non-vegans was noted for vitamin B12, which Dr. Weikert's team found noteworthy because the vegan diet tends to be low in vitamin B12, just as it is in iodine. However, 92 percent of the vegans in the study reported regularly taking B12 supplements. By contrast, only five of the vegans reported taking iodine supplements.

Accordingly, the study authors concluded there may be a lack of awareness of the need to supplement the vegan diet with iodine. Given iodine's role in metabolism and weight control, raising that awareness could prove to be game-changing for vegans discouraged by unexpected weight gain. That being said, here are 6 things you need to know before adding supplements.

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Lauren Cahn
Lauren Cahn is a food, health, and culture writer whose work has appeared online and in print for Reader's Digest as well as Health Digest, Huffington Post, Taste of Home, and others. Read more about Lauren