There are two “S” words in nutrition that have a good side and a dark side: soy and sugar. Both have exceptions of when they can be brought into your diet—but, for the most part, they are bad news for your digestion, wellness, and metabolism. To understand these two troublemakers, we sat down with registered dietitian Farah Fahad to get a better sense of why soy and sugar wreak havoc on our bodies—and when it’s ok to let them in our mouths.

You say most soy is bad news, why?
More than 90 percent of the soy grown in the U.S. is now genetically modified. Most of the soy on the market is heavily processed in the form of soybean oil, soy milk, soy cheese, soy butter, and soy protein is also used in a lot of “fake meat products.” This type of processing is not metabolized well by the body and can cause inflammation.

Thousands of studies link soy to malnutrition, digestive distress, immune system breakdown, thyroid dysfunction, cognitive decline, reproductive disorders and infertility — even cancer and heart disease. Genetically engineered soy can cause allergies, sterility, birth defects, and offspring death rates up to five times higher than normal.

Soybean crops are also heavily sprayed with chemical herbicides, such glyphosate, which is carcinogenic. So, by eliminating soy, you are protecting your body from harmful outcomes. Soy is higher in phytoestrogens than just about any other food source.

OK— what are phytoestrogens and why are they important to our wellness?
Phytoestrogens are plant-based estrogens that mimic estrogen in our bodies and in excess can cause a myriad of problems. Soy is also goitregenic (thyroid suppressing). Goitrogens work by preventing your thyroid from getting the necessary amount of iodine. Thyroid imbalance can cause weigh gain and affect metabolism. Soybeans — even organically grown soybeans — naturally contain “anti-nutrients.” Anti-nutrients get in the way of your body benefiting from soy.

We heard that fermenting soy products makes them healthier to eat—is that true?
Yes. Fermenting destroys these anti-nutrients, allowing you to reap the benefits. These organic fermented soy products are beneficial in moderation: Miso, Tempeh, Natto, and Soy sauce (as long as it’s fermented in the traditional way, and not all are).

Looks like sushi night is back on! Let’s talk about sugar…
When you think of sugar, you may think of just white sugar- but sugar is in so many products, from ketchup to bread to peanut butter. That is why it is important to read labels. I recommend eliminating all excess hidden sugars as well as sugary drinks. And if possible white sugar.

What about healthy sweets?
Fruits are allowed, as well as raw or Manuka honey as I feel like these are the most natural forms.

What happens to our bodies when we consume bad sugar?
Sugar in excess pushes fat storage and can cause weight gain. Sugar is empty calories, meaning it’s high in calories and low in nutrients. Sugar can also cause mood swings and is more addictive than cocaine.

And if we ditch it from our system?
Eliminating excess sugar will avoid blood sugar crashes, cravings, better skin, digestion, and inevitably [lead to] weight loss.