Artificial Sweeteners When Trying to Conceive or Pregnant: Bad Idea?

Note: I interpret scientific studies, but my interpretation is not medical advice.

Ditch sugar for artificial sweeteners?

Sugar is a simple carbohydrate that's very high on the glycemic index, and as I've covered before, it's worth limiting sugary foods (including high fructose corn syrup, maple syrup, and honey) when trying to conceive. But we're all human, and humans like sweet things. So what about low-calorie sweeteners instead -- do they influence fertility, and are they safe to use while trying to conceive and once you're pregnant? A lot has been written about artificial sweeteners and general health, but far less is known specifically about fertility. Let's go through the evidence so you can make an informed call.

Saccharin (Sweet 'N Low)

Fertility: One study gave female rats a daily dose of saccharin for 48 straight days and found changed hormonal feedback: longer estrous cycles, higher progesterone, more ovarian cysts, and weight gain -- a symptom cluster that closely resembles PCOS, as the researchers themselves noted. The rats received 10-50 times the FDA's acceptable daily intake, so odds are you'll be fine at normal levels, but it's worth keeping an eye on products containing it.

Pregnancy: Saccharin crosses into the fetal bloodstream through the placenta, and takes much longer to clear from a fetus than from your own body. High-dose mouse studies found no fetal malformations, and comparisons of women who did and didn't consume saccharin found no difference in spontaneous abortion rates. The old bladder-cancer scare traced back to a single rat study; all later research, including extensive human studies, found no link. Saccharin is broadly safe at typical intake -- but the combination of hormone effects in animal studies and easy placental crossing is reason enough for me to suggest limiting it.

Aspartame (Equal, NutraSweet)

Fertility: Aspartame is probably the most widely used sweetener and one of the most controversial, but the general scientific consensus is that it's safe in the amounts people actually consume -- you'd need more than three 2-liter bottles of diet soda in a day to exceed the FDA limit. Fertility-specific research is surprisingly sparse; in one of the few recent studies, obese female rats given a dose equivalent to about 2 cans of diet soda showed no obvious negative effect on their ability to conceive.

Pregnancy: Aspartame is considered safe in pregnancy at several times the FDA limit, largely because it doesn't enter your bloodstream at all -- it's broken down in the gut into aspartic acid, phenylalanine, and methanol, none dangerous in moderate amounts (aspartic acid to those without the rare condition PKU). Some in-vitro studies (tested outside the body, in a test tube) have raised alarm about DNA effects, but since aspartame never reaches your bloodstream in the first place, those findings don't translate to real exposure. Large studies with thousands of participants, including pregnant women, find no association with DNA damage or cancer.

Sucralose (Splenda)

Fertility: No human studies exist specifically on sucralose and fertility, but animal data is reassuring: rats fed 100+ times the expected human daily intake showed no change to estrous cycles, mating behavior, or "mating performance" (their term, not mine). Most sucralose isn't even absorbed by your body -- it passes through largely unmetabolized.

Pregnancy: The same rat study found no negative effects on gestation, maternal or fetal viability, fetal development, birth, or lactation, even at very high doses.

Stevia

Fertility: This is the one with a genuine yellow flag. One well-designed study gave obese rats a dose of stevia well within the human acceptable range (about what you'd get from a single can of Zevia). Non-obese, unfed-stevia rats had a 100% conception rate; obese rats fed aspartame had 80%; but obese rats fed stevia had only 53% -- you could almost call it mildly contraceptive. A much older 1960s study found similarly reduced conception in stevia-fed mice, though at far higher doses than any human would consume. Several other animal studies found no anti-fertility effect at all, so the picture isn't settled -- but given you're actively trying to optimize your odds, it's reasonable to limit stevia for now.

Pregnancy: In the rat study above, the rats that did conceive went on to a 100% birth rate, so it doesn't appear harmful once pregnant. There's no human pregnancy data either way.

Acesulfame Potassium (Ace-K)

Fertility: Not much research exists specifically on Ace-K and fertility. One 1980 study gave rats extremely high doses (1-3% of their diet, equivalent to eating more than an ounce of pure sweetener) across several generations and found no change in litter size, birth weight, or mortality -- growth rate was slightly reduced at the highest dose.

Pregnancy: Ace-K crosses into amniotic fluid and breast milk. One mouse study found prenatal/postnatal exposure led to a stronger preference for sweet foods in adulthood, and a human study found both Ace-K and sucralose showed up in breast milk 2-5 hours after a woman drank a diet soda containing them. It's not clearly dangerous, but limiting it is a reasonable precaution.

Cyclamate

Fertility: Banned in the US since 1970 (originally over a since-discredited cancer link, based on a rat study using doses equivalent to 550 cans of diet soda a day), but legal in Europe, Australia, and Asia. A 1975 study adding 1% cyclamate to mouse diets -- an unrealistically high dose -- found no change in conception or miscarriage rates. A 2003 human study found no link with male fertility either.

Pregnancy: High-dose rat studies from the late 1960s found no difference in litter size, fetal weight, or malformations. It does cross the placenta and accumulate in the fetus, so if you have access to it outside the US, it's probably best to limit it -- though if you're in the US, this is moot, since it's banned anyway.

Which to avoid and which are OK

• Saccharin: limit or avoid -- possible hormone disruption, crosses the placenta
• Aspartame: OK in moderation
• Sucralose: OK in moderation
• Stevia: limit or avoid -- animal studies suggest a possible fertility effect
• Ace-K: limit or avoid -- crosses the placenta and into breast milk
• Cyclamate: limit or avoid -- crosses the placenta (moot if you're in the US, where it's banned)

Final thoughts

Before you clear out your pantry: all of these sweeteners are FDA-approved for human consumption, including during pregnancy. I'm not telling you what to do -- but if you want to optimize your fertility as much as possible, it might be worth a look at what's in your kitchen. If you'd rather not cut sweeteners out entirely, that's fine too; just stay below the FDA's acceptable daily intake limits, which are set generously high.

References

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