A new study followed 380 pregnant women to see how their eating habits affected their weight gain during pregnancy. Researchers found that women who improved their diet quality as pregnancy progressed—by eating more seafood, nuts, beans, and whole grains while cutting back on refined grains—gained less weight than those whose diets didn’t improve. This effect was strongest in women who started pregnancy at a higher weight. The findings suggest that making gradual improvements to what you eat during pregnancy, rather than trying to diet strictly, may help keep weight gain within healthier ranges.

The Quick Take

  • What they studied: Whether improving the quality of foods a pregnant woman eats during pregnancy is connected to how much weight she gains
  • Who participated: 380 pregnant women from Illinois who were followed from early pregnancy through delivery. The study included women of different weights before pregnancy, including those with obesity
  • Key finding: Women with obesity who improved their diet quality by 10 points (on a 100-point healthy eating scale) gained about half a standard deviation less weight than expected. This improvement came from eating more seafood, beans, nuts, and whole grains, and fewer refined grain products
  • What it means for you: If you’re pregnant and want to manage weight gain, focusing on eating better-quality foods—especially more plant proteins, seafood, and whole grains—may help more than simply eating less. This appears most helpful for women starting pregnancy at a higher weight

The Research Details

This study used information from a larger, long-term research project called the Illinois Kids Development Study that followed pregnant women from 2013 to 2018. Researchers asked women to report what they ate during two time periods: around 13 weeks pregnant and around 35 weeks pregnant. They used a detailed food questionnaire to calculate how healthy their overall diet was using two different scoring systems (the Healthy Eating Index and the Alternative Healthy Eating Index). They then looked at how much their diet quality improved between these two time points and compared it to how much weight they gained during pregnancy. The researchers used special calculations to account for each woman’s starting weight and how far along she was in pregnancy, so they could fairly compare weight gain across different women.

Previous studies only looked at individual foods or nutrients, not whether eating patterns improved over time. This study is important because it shows that getting better at eating healthy foods as pregnancy progresses—rather than maintaining the same diet throughout—is what matters for managing weight gain. This is more realistic and encouraging than expecting women to follow strict diets during pregnancy

The study included a good-sized group of 380 women followed throughout their pregnancies with actual weight measurements. The researchers carefully adjusted their analysis to account for total calories eaten and other factors that could affect results. However, women reported their own food intake, which can be less accurate than other methods. The study was conducted in one region of Illinois, so results may not apply equally to all populations

What the Results Show

For women with obesity, each 10-point improvement in diet quality (on a 100-point scale) was linked to gaining about 0.55 standard deviations less weight than expected based on international guidelines. This improvement came mainly from eating less refined grain products (like white bread and regular pasta) and more seafood and plant-based proteins (like beans and nuts). When researchers looked at a different diet quality measure, they found similar results—a 10-point improvement was linked to gaining about 0.48 standard deviations less weight, driven by higher intake of nuts and legumes. These associations held even after accounting for total calories eaten, suggesting that the type of food matters, not just the amount. The effect was strongest in women who started pregnancy with obesity, with smaller or no clear effects in women who started at healthy or overweight levels.

The study found that the specific foods driving the improvement differed slightly depending on which diet quality measure was used, but both pointed to the same general pattern: eating more plant-based proteins and seafood while reducing refined grains was protective against excess weight gain. The fact that these associations remained strong even after accounting for total energy intake suggests that diet composition—what you eat—matters more than simply eating fewer calories

This research builds on earlier studies that looked at individual foods or nutrients during pregnancy. By examining how diet quality changes over time, this study provides a more complete picture than previous work. It aligns with general nutrition science showing that diet quality matters for weight management, but extends this to the specific context of pregnancy in women with obesity, a group at higher risk for pregnancy complications

Women reported their own food intake using questionnaires, which may not be perfectly accurate. The study only included women from one area of Illinois, so findings may not apply to all populations or ethnic groups. The study was observational, meaning researchers observed what happened naturally rather than randomly assigning women to different diets, so we cannot be completely certain that diet improvements caused the lower weight gain rather than other factors. The study did not examine whether these weight gain differences led to better health outcomes for mothers or babies

The Bottom Line

If you are pregnant or planning pregnancy and have obesity or overweight, consider gradually improving your diet quality by eating more seafood, beans, nuts, whole grains, and vegetables while reducing refined grain products. This appears to help manage weight gain during pregnancy. This is a moderate-confidence recommendation based on this single study. Discuss specific dietary changes with your healthcare provider or a registered dietitian who specializes in pregnancy nutrition

This finding is most relevant for pregnant women with obesity or overweight who are concerned about managing weight gain. Women at healthy weights before pregnancy may see different results. All pregnant women should work with their healthcare team on nutrition, as pregnancy has unique nutritional needs. This research is also relevant for healthcare providers and dietitians counseling pregnant women

Diet quality improvements appear to be associated with lower weight gain throughout pregnancy, with the study measuring changes from early pregnancy (13 weeks) to late pregnancy (35 weeks). Benefits would likely develop gradually over weeks to months as eating patterns improve

Want to Apply This Research?

  • Track weekly servings of seafood, beans/legumes, nuts, and whole grains consumed, plus refined grain products reduced. Aim to increase healthy protein sources by 1-2 servings per week and reduce refined grains by a similar amount
  • Set a specific goal like ’eat fish or seafood 2 times per week’ or ‘swap white bread for whole wheat bread at 3 meals per week.’ Use the app to log these specific swaps and track progress over 2-4 week periods
  • Review diet quality improvements monthly using a simple checklist of healthy foods eaten more often and refined grains eaten less often. Track weight gain at regular prenatal appointments and compare to expected ranges for your stage of pregnancy. Celebrate improvements in food choices rather than focusing only on weight numbers

This research suggests associations between diet quality improvements and lower weight gain in pregnant women with obesity, but does not prove that diet changes directly cause lower weight gain. Pregnancy nutrition is complex and individual needs vary greatly. All pregnant women should work with their healthcare provider or a registered dietitian for personalized nutrition advice. This information is not a substitute for medical care. Weight gain during pregnancy is normal and necessary; the goal is healthy gain within recommended ranges for your individual situation. Do not attempt to lose weight during pregnancy without medical supervision.