If you’ve got a little one on the way, or are thinking about adding to your family soon, you’re probably already focusing on your baby’s health and nourishment (#momlife). Which brings the conversation to your own nutrition: What if you are looking to lose weight before getting pregnant and want to try a diet of the moment, such as intermittent fasting (IF)? Or maybe you're curious about it's purported longevity or blood sugar benefits.
Whatever the reason is behind your IF interest, you might be curious about how to maintain those eating patterns during your actual pregnancy. Or, perhaps you just found out you’re pregnant and want to know the safest way to continue or wean yourself off of a fasting diet.
Yep, these are questions and concerns that docs and prenatal nutritionists hear from expectant mamas these days, given all the hype surrounding fasting diets right now. So here's the lowdown on intermittent fasting for pregnant women—with input from Jennifer Wu, MD, an ob-gyn at Lenox Hill Hospital in New York City, and Nicole German Morgan, RDN, LD, CLT, a dietitian with a background in prenatal nutrition.
And, as always, experts advise you to always check in with your health-care provider before making any dietary changes, especially if you’re newly pregnant or planning to get pregnant.
Let's get right to it: Is intermittent fasting ever safe for pregnant women?
Generally, fasting isn’t recommended for pregnant women. While research shows that intermittent fasting can benefit metabolism, lead to weight loss, and may potentially reduce the risk of developing type 2 diabetes, it can actually lower a pregnant woman’s blood sugar too much. “Low blood sugar in combination with the natural drop in blood pressure in pregnant women could lead to lightheadedness and fainting,” says Dr. Wu.
An older study that focused on religious intermittent fasting in pregnant women (with healthy pregnancies) found that fetal movement was lower when mothers were fasting. This makes sense, because her glucose levels would be low, and fetal movement is tied to how much glucose (aka an energy source for the bod) the fetus is able to get from the mother. That's why most religious fasting gives an exemption to pregnant women, Dr. Wu adds.
So, intense fasting is a no-go for pregnant women (more on that later). But the only type of fasting that may be safe for women who aren’t too far along in pregnancy is an overnight fast, for about 12 hours maximum. But, even doing a 12-hour fast depends on the trimester, explains Morgan.
During the early stages of the first trimester, it’s of course essential to focus on consuming enough important prenatal nutrients, but your body may not need that many more additional calories than your normal intake. “In the third trimester, and the later stages of the second trimester, intermittent fasting may not be appropriate at all—many women will require an additional evening snack prior to bedtime, or need to eat quickly upon waking,” Morgan explains.
You need to make sure that you are getting enough of the essential nutrients as well as calories (many pregnant women are advised to add about 300 extra calories a day), especially if you start out your pregnancy underweight or even at normal weight, so restricting your eating may not be the right solution, she adds.
Are certain types of intermittent fasting safer than others when you’re pregnant?
If you’re early on in the pregnancy, doing a modified version of intermittent fasting, by fasting overnight for about 12 hours (as mentioned) would be your only moderately safe option. According to Morgan, this would involve fasting from about 7 p.m. or 8 p.m. at night to 7 p.m. or 8 a.m. the next morning, which might be your normal eating schedule anyway.
But, you don’t want to cram too many calories into a short period of time, as that isn’t healthy for digestion, or miss out on calories necessary to nourish the baby by spacing out your eating too much, she points out. The other popular versions of IF schedules—the 16:8 diet (where you eat within an eight-hour window), the 5:2 method, which involves eating normally five days a week and pulling back on calorie intake substantially two days a week, or alternate-day fasting—should all be off-limits, as they’re too extreme for any pregnant women.
Eating schedules are really different for everyone. But Dr. Wu generally recommends eating more frequently when you're pregnant instead, with small meals about every two to three hours, especially during the first trimester, when morning sickness is prevalent and you may not be in the mood to eat a huge meal at one time. “This also helps to keep the blood sugar steady in the second and third trimesters,” Dr. Wu says.
But for patients who struggle with heartburn during pregnancy, Dr. Wu suggests stopping eating about four hours before going to sleep to allow more time for digestion, since heartburn may be worse once you lie down in bed. If you follow those guidelines, you may not tend to eat until breakfast upon waking up, so it is actually somewhat similar to an IF schedule.
If I practiced intermittent fasting before pregnancy, should I just stop and return to a normal eating schedule?
Yep, you want to eat more frequently, without large chunks of time without nutrients. Here's why: Eating more frequently helps keep your blood sugar and blood pressure—and the baby’s—stable. “To promote more [weight] maintenance and less weight loss, it may be smart to widen your window of eating in order to be able to consume a more balanced diet,” Morgan says.
Does intermittent fasting affect fertility?
Believe it or not, if you’re trying for a baby, IF could help in some circumstances. “If patients are overweight or obese, they may have irregular cycles and trouble ovulating,” which can make it tough to get pregnant. So following an IF diet (which typically means you'll be restricting your calorie intake) may yield weight loss, and in turn, improve fertility.
For example: Women with polycystic ovary syndrome—or PCOS, which often disrupts metabolism, the menstrual cycle, and ovulation—may encounter fertility issues. But, as one study showed, losing weight (by reducing calorie intake generally by 500 to 1,000 calories per day) may help overweight women with PCOS produce luteinizing hormone, and in turn, ovulate more regularly (and therefore get pregnant more easily). Dr. Wu asserts that IF is fine for weight loss, but that you should stop dieting upon finding out that you’re pregnant.
On the other end of the spectrum, if you’re underweight, continuing to restrict your eating and calorie intake can be detrimental to fertility. In extreme cases, “intermittent fasting and losing weight may actually adversely affect fertility as patients may stop menstruating and ovulating,” Dr. Wu says. Morgan adds that eating less frequently while practicing IF can put the body under high stress, which is not helpful when it comes to getting pregnant. “The most important point for fertility is to nourish the body in a balanced way, and not to let the body feel as if it is under stress,” says Morgan.
Is it ever safe to lose weight at all during pregnancy, via a fasting diet or any other diet?
In short, no. Weight loss is, in general, not a thing you want to focus on at all during pregnancy. So you want to speak to your doctor about potentially terminating a particular diet you're on to make sure you're approaching pregnancy safely for you and the baby.
During pregnancy, it's more about staying at a healthy weight, or not gaining too much weight during the pregnancy if you’re overweight. “If patients are overweight or obese when they become pregnant, the recommendation is to gain less weight, around 15 to 20 pounds, depending on the weight of the patient,” Dr. Wu says.
But even if the patient is overweight, or develops gestational diabetes during pregnancy, for instance, fasting still isn’t the answer, because it could interfere with any blood sugar-regulating medication the patient is on, she notes.
Of course, there are many factors that can impact your weight during pregnancy, and it also depends on the trimester you’re in. For example, it’s normal for women to drop a few pounds during the first trimester from morning sickness, nausea, or even hyperemesis gravidarum. It's not a good idea to lose any weight at all during the second or third trimester, Morgan says. But ultimately the advised amount of weight gain during pregnancy depends on the patient and is something you should discuss at length with your doctor so that you feel informed and comfortable.
The bottom line: Nutrition during pregnancy is highly individualized to the person, how high-risk the pregnancy is, and the prior health conditions of the mother—after all, no one person’s body or metabolism is the same. Before trying any new diet or changing your eating habits, it’s important to check in with your healthcare provider to ensure that it’s safe and sustainable for you to continue throughout pregnancy.
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