【Protecting Mom and Baby】The Risks of Overeating During Pregnancy, Weight Management Tips, and Key Points for Your Diet

“I thought I had to eat for two for the baby’s sake, and I just couldn’t stop snacking…”

“How careful do I really need to be about what I eat during pregnancy? It all seems so complicated.”

“My child developed atopic dermatitis, and I keep wondering whether it was because of what I ate while I was pregnant…”

These are worries I hear a lot from expecting moms.

When it comes to eating during pregnancy, the focus tends to be all on “eating well for the baby,” but I feel that not many people know that overeating and unbalanced eating habits may affect a child’s constitution for life.

In this article, based on what recent research has been finding, I’ll explain as simply as I can how overeating during pregnancy relates to a child’s risk of obesity and allergies.

This is also useful for anyone who’s trying to conceive, so please read through to the end.

How Does Overeating During Pregnancy Affect the Baby?

During pregnancy, the baby in your womb grows while receiving nutrients from your blood.

But it’s not just about delivering nutrients.

Recent research has been showing that a mother’s eating habits may influence the very “blueprint” of the baby’s body.

This is called “fetal programming.”

It’s the idea that the environment in the womb shapes a person’s constitution and susceptibility to disease after birth.

You could think of the womb as a workshop where the “blueprint” of the baby’s body is being drawn up.

It’s thought that if the materials (nutrients) delivered to that workshop are too plentiful or too scarce, it can affect how the blueprint gets drawn.

High Blood Sugar May Affect the Baby’s Metabolism

If you eat too many sweets or refined carbs (white rice, white bread, snacks, soft drinks) during pregnancy, your blood sugar tends to rise again and again.

When this high blood sugar continues, excess glucose also reaches the baby through the placenta.

What happens then is that the baby’s pancreas may be made to work harder than necessary while still in the womb, essentially being “trained” to release large amounts of insulin.

As a result, there are research reports suggesting that after birth, the baby’s insulin secretion and sensitivity may be more easily thrown off, and the risk of obesity and diabetes later in life may increase.

The first place I read about this was in a book about fasting.

There was a line saying that “the food environment in the womb shapes that child’s metabolism for life,” and it stopped me in my tracks.

It’s not something I can ever experience myself, but that’s exactly why I want as many people as possible to know about it.

The Link Between Gestational Diabetes and the Baby’s Body Size

Have you heard of a condition called “gestational diabetes”?

It’s a condition that first appears during pregnancy, in which blood sugar becomes harder to control.

During pregnancy, your body is naturally in a state where blood sugar rises more easily, so that sugar can be delivered to the baby.

When overeating is added on top of that, insulin, the hormone that lowers blood sugar, can easily fall behind.

Insulin is like a “delivery worker” that carries sugar from your blood into your cells.

If there are too many packages (sugar), the delivery workers can’t keep up, and sugar overflows in the blood.

Diet isn’t the only factor in whether you develop gestational diabetes, but there’s no doubt that your everyday eating habits play a big role.

Make your regular checkups a priority, and keep the quality of your meals in mind.

Gestational diabetes often has few noticeable symptoms, so it’s usually found through a blood test at a prenatal checkup.

Even if you’re diagnosed, you’ll work on controlling your blood sugar by adjusting your diet under the guidance of your doctor and a registered dietitian.

Why Do People Overeat During Pregnancy?

Overeating during pregnancy is never simply a matter of weak willpower.

That’s because all sorts of changes are happening inside your body as it nurtures your baby.

First, let’s look at the reasons that can easily lead to overeating.

Hormonal Changes Increase Your Appetite

When you become pregnant, your body starts releasing large amounts of hormones that help sustain the pregnancy.

These hormones are said to sometimes increase your appetite or change your food preferences.

You can picture it as your body getting ready, thinking, “Let’s store up nutrients for the baby.”

“Hunger Sickness”: When an Empty Stomach Makes You Feel Awful

Besides the type of morning sickness where nausea gets intense, there’s also a type sometimes called “hunger sickness,” where you feel sick whenever your stomach is empty.

During this phase, you feel unwell unless you have something in your mouth, so the number of times you eat and the amount you eat tend to go up.

During this time, rather than forcing yourself to hold back, it’s important to find foods you can eat in small amounts at a time.

The Rebound After Morning Sickness and the “Eating for Two” Myth

Once they get through the morning sickness phase, quite a few people find their appetite suddenly comes roaring back.

As a rebound from not being able to eat until then, you might eat as much of your favorite foods as you like and gain weight quickly.

The belief that “I have to eat for two” is another common cause of overeating.

Stress and Lack of Exercise

Between changes in how you feel physically, worries about giving birth, and concerns about work or family, pregnancy is also a time when stress builds up easily.

When stress piles up, it’s natural to want to soothe it with sweets or convenient snacks.

On top of that, as your belly grows, you get fewer chances to move your body, and you tend to burn less energy.

When days without movement continue, your mood can sink more easily too, which can lead to a vicious cycle of more overeating.

In this way, overeating during pregnancy is often the result of hormones, morning sickness, and physical and emotional changes all overlapping.

Eating Patterns During Pregnancy That Can Lead to Childhood Obesity

Being mindful that “I need to eat during pregnancy” is important, but what you eat and how much can make a big difference in the effects on your child.

Here are some eating patterns that research has flagged as needing particular attention.

If any of them sound familiar, I’d like you to try adjusting them little by little.

Eating Too Many Refined Carbs and Processed Foods

White rice, white bread, sugar, snacks, and soft drinks.

If you eat a lot of these on a daily basis, you’re more likely to experience “blood sugar spikes,” where your blood sugar repeatedly shoots up and then crashes.

If this continues during pregnancy, it’s thought that it may affect how the baby’s metabolism gets set.

Researchers have also pointed out the risk that insulin resistance (a state in which insulin doesn’t work well) may start forming as early as the fetal stage.

Unbalanced Fats (Too Much Omega-6)

Modern diets tend to contain too much “omega-6 fatty acids,” found in fried foods, margarine, packaged snacks, and the like.

When the balance between omega-6 and omega-3 is thrown off, inflammation is more likely to occur in the body, and this may also affect the development of the baby’s immune system.

Making a point of getting omega-3s from oily fish (mackerel, Pacific saury, sardines) and nuts can help support a healthy gut environment while laying the foundation for your baby’s immunity.

Excess Weight Gain from Too Many Calories

There’s an appropriate range for weight gain during pregnancy (it varies depending on your BMI; roughly 7–12 kg (15–26 lb) has long been the general guideline, but the new guideline issued in 2021 by the Japan Society of Obstetrics and Gynecology revised it to about 10–13 kg (22–29 lb) for people of normal weight).

Going well beyond that is said to make it more likely that the baby will have too much body fat.

In other words, a paradoxical situation can arise where eating too much “for the baby’s sake” ends up giving the baby a tendency toward obesity.

Shifting your mindset to focus on quality over quantity may be the best shortcut.

Look at the “Pace” of Weight Gain, Too

If you’re not sure what your own guideline is, check your maternal health handbook or ask your doctor or midwife at your checkup.

When it comes to weight, it’s important to look not only at how much you gain in total but also at how quickly you’re gaining it.

If your weight shoots up over a short period, there may be other causes besides overeating, such as swelling.

Weighing yourself at the same time every day and keeping a record makes it easier to talk things over with your doctor or midwife at your checkups.

Overeating Also Takes a Toll on Mom’s Body

Gaining too much weight can put all sorts of strain on your own body as well.

Hypertensive disorders of pregnancy are conditions in which blood pressure becomes high during pregnancy.

Obesity before pregnancy and excessive weight gain during pregnancy are considered among the factors that raise the risk of these conditions.

When high blood pressure persists, it can affect not only your body but also the function of the placenta, which delivers nutrients to your baby.

Also, gaining weight quickly makes common pregnancy discomforts, like back pain, swollen legs, and constipation, more likely.

It’s also not unusual for weight gained during pregnancy to be hard to lose after giving birth, leading to ongoing concerns about body shape and health.

If you notice any worrying symptoms, don’t wait for your next checkup; contact your OB-GYN.

Eating Too Little or Restricting Food on Your Own Is Also a No-Go

On the other hand, if you don’t gain enough weight during pregnancy, the risk of having a “low birth weight” baby is said to increase.

During pregnancy, you need just the right balance: “not too much, not too little.”

Even if you’re worried about your weight, avoid dieting or skipping meals on your own during pregnancy.

If you’re concerned about how much weight you’re gaining, rather than cutting back on food yourself, it’s important to talk to your doctor or midwife first.

The Surprising Influence of Diet on Allergies and Immune Development

I sometimes hear people say, “My child developed atopic dermatitis, and maybe it was because of what I ate while I was pregnant.”

That may not be entirely off the mark.

Your Gut Environment During Pregnancy Affects Your Child’s Allergies

It’s said that the balance of the trillions of bacteria living in your gut (gut bacteria) has a major influence on how the immune system develops.

It’s also said that about 70% of the body’s immune cells are concentrated in the gut.

A mother’s gut environment during pregnancy is passed on to the baby at birth.

As the baby passes through the birth canal, it receives the mother’s gut bacteria, and these become the foundation of the child’s own gut environment.

In other words, getting fiber and fermented foods during pregnancy to support a healthy gut environment may also help prevent allergies in your child.

Simply making a point of eating nukazuke (Japanese rice-bran pickles) or yogurt during pregnancy might be a gift to your baby.

You don’t need to overthink it.

Isn’t it heartwarming to think that small habits, built up over time, are laying the foundation for your child’s immunity?

How overeating disrupts your gut environment is explained in detail in another article, so please take a look if you’re curious.

Eating a Wide Variety of Foods May Help Prevent Allergies

Some studies report that eating too much of certain foods during pregnancy raises the risk of allergies, while others report that eating a wide variety of foods lowers the risk.

It seems fair to say that what matters is not so much avoiding particular foods as eating a balanced and varied diet.

If allergies run in your family and you’re worried, please talk to your doctor.

The Link Between C-Sections and Gut Bacteria

Babies born by C-section don’t pass through the birth canal, so they’re less likely to receive their mother’s gut bacteria.

Some studies suggest that, as a result, their risk of allergies and asthma may be slightly higher.

However, this often isn’t something you can choose, so it’s important to make up for it through “breastfeeding after birth” and “caring for the baby’s own gut environment.”

What Is Fetal Programming (Epigenetics)?

Have you ever heard the word “epigenetics”?

It refers to the mechanism by which, even though your genes themselves can’t be changed, the way your genes are “read” can change depending on your diet and lifestyle.

Diet Flips Your Genetic Switches

We all have a wide variety of genes in our bodies.

There are genes that make us more prone to obesity and genes that make inflammation more likely, but just having them doesn’t mean they’ll necessarily be activated.

Whether those switches turn ON or OFF depends on “the environment we grow up in.”

To use the analogy of room lighting, the light bulb (gene) may be the same, but whether you flip the switch changes how bright the room is.

And one of the most important periods for that “environment” is the time spent in the womb.

It’s said that a mother’s diet during pregnancy affects the baby’s gene expression and may raise or lower the risk of obesity, diabetes, allergies, and more later in life.

This may sound scary, but flip it around and it also means “by changing what you eat now, you may be able to change your child’s future for the better.”

Eating Habits Before Pregnancy Matter Too

From an epigenetic perspective, it’s been pointed out that eating habits not only during pregnancy but also before pregnancy may have an effect.

If your menstrual cycle is irregular or you’re struggling with hormone balance, please also check out my article on the relationship between fasting and hormone balance.

It explains in detail how fasting affects the hormonal system.

Effects Across Generations (the Intergenerational Effect)

Even more surprising, there’s research suggesting that epigenetic changes may be passed down across generations.

In other words, your eating habits might affect not only your children but even your grandchildren.

Hearing this, I imagine many of you are feeling the importance of diet all over again.

Frequently Asked Questions About Overeating and Eating Habits During Pregnancy

For Your Child’s Future and Your Own, Start Rethinking Your Food Choices Today

I hope I’ve been able to get across that overeating and unbalanced eating habits during pregnancy may be linked to a child’s risk of obesity and allergies.

This isn’t meant as a scare tactic, as in “there are foods you must never eat during pregnancy.”

Instead, I’d be happy if you took it as a positive message: “Just by changing your eating habits a little, you can help protect your child’s health and your own.”

3 Things You Can Start Easily Today

If you’re anxious about how much weight you’re gaining or how much you’re eating, don’t struggle alone; talk to your doctor or midwife.

Fasting After Giving Birth as an Option

Fasting during pregnancy absolutely requires consulting your doctor, but incorporating fasting to improve your health before pregnancy and after giving birth (but not during pregnancy) is a very effective option.

Intermittent fasting (16-hour fasting) is expected to help balance hormones, improve your gut environment, and help restore insulin sensitivity.

If you want to improve your body shape or overall health after giving birth, I’d really like you to give it a try.

However, the right way to eat depends on how your body is recovering after childbirth and on your breastfeeding situation, so be sure to talk to your doctor before you start.

Also, when it comes to the effects on your child, I’d like you to know about the connection between immunity and eating habits, which builds up from everyday eating.

I’d be glad if this gives you some ideas for building good health for the whole family.

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