Independent report

Nutrition and maternal weight outcomes: SACN report summary

Published 3 February 2026

Introduction

UK dietary recommendations for women of childbearing age and those who are pregnant or breastfeeding are based on advice from the Scientific Advisory Committee on Nutrition (SACN) and its predecessor, the Committee on Medical Aspects of Food and Nutrition Policy (COMA).

Longstanding NHS advice on a healthy diet in pregnancy is generally the same as for the UK population. That is, pregnant women should eat a healthy, balanced diet as depicted in the UK’s national food model, the Eatwell Guide. Women do not need a special diet during pregnancy or while they are breastfeeding, other than:

• avoiding some specific foods and drinks (as set out in the NHS advice on foods to avoid in pregnancy)
• following advice on folic acid and vitamin D (as set out in the NHS advice on vitamins, minerals and supplements in pregnancy)

Physical changes and other factors may influence eating patterns during pregnancy. For example, women may feel sick or vomit, or they may have food cravings or aversions.

In the last 3 months of pregnancy, women need around an extra 200 kilocalories (kcal) a day above their usual requirements.

Women who are exclusively breastfeeding need around an extra 330 kcal a day above their usual requirements for the first 6 months after birth. This assumes they are losing about 0.8kg each month of the weight they gained during pregnancy. Breastfeeding, in particular exclusive breastfeeding, is associated with greater weight loss after pregnancy (known as postpartum weight loss).

Ideally, women should begin pregnancy at a healthy body weight. The National Institute for Health and Care Excellence (NICE) guideline Maternal and child nutrition: nutrition and weight management in pregnancy, and nutrition in children up to 5 years (NG247) highlights that women “do not need to ‘eat for two’ … during pregnancy”. However, intentional weight loss during pregnancy is not recommended because of potential adverse effects on the baby.

Women living with overweight or obesity are at an increased risk of pregnancy-related health complications, such as gestational diabetes. Women living with severe obesity are at greatest risk. Living with underweight can also increase the risk of health complications in pregnancy for the mother and baby.

Gaining weight during pregnancy, known as gestational weight gain (GWG), is a normal part of pregnancy. It reflects the growth of the baby and physical changes in the mother. GWG is an important indicator of an individual’s risk of adverse pregnancy outcomes, particularly where women are living with overweight or obesity. However, the mother’s body mass index (BMI) (measured before or at the start of pregnancy) is likely to have a greater influence on the health of the mother and baby than the amount of weight gained during pregnancy.

In the USA, guidelines on appropriate weight gain during pregnancy have been published by the National Academy of Medicine (NAM), formerly the Institute of Medicine (IOM). These guidelines are based on maternal BMI before pregnancy and are used by many health professionals and researchers to assess GWG. There are currently no UK guidelines for ‘appropriate’ GWG. However, NICE NG247 highlights that if people are interested in monitoring their weight change during pregnancy, they can refer to the NAM guidelines.

Approach to the assessment

This is the first of 2 publications on SACN’s risk assessment on nutrition and maternal health.

The terms of reference were to:

• review the scientific basis of current UK dietary recommendations for women before pregnancy, during pregnancy and up to 24 months after delivery
• make recommendations based on the review of the evidence

This report covers nutrition and maternal weight outcomes during pregnancy and after giving birth (referred to as ‘postpartum’). A future SACN position statement will consider wider UK dietary recommendations for women of childbearing age. This report covers girls and women aged 14 to 49 years, referred to in this report as ‘women of childbearing age’, unless a specific age group is being considered.

Clinical management is outside SACN’s remit and is under the remit of NICE. This SACN report should be read alongside the NICE guidelines:

• Maternal and child nutrition: nutrition and weight management in pregnancy, and nutrition in children up to 5 years
• Overweight and obesity management

Assessment of the evidence for this report is consistent with the ‘SACN framework for the evaluation of evidence’, available on the SACN webpage. The assessment was informed by:

• previous assessments undertaken by SACN, in particular the 2011 SACN Dietary Reference Values for Energy report
• survey data on the prevalence of overweight and obesity in both pregnant and non-pregnant women of childbearing age
• evidence on dietary intakes and nutritional status of women of childbearing age from the UK National Diet and Nutrition Survey (NDNS) and modelled estimated energy intakes based on Health Survey for England body height and weight data
• systematic reviews and meta-analyses of randomised controlled trials and prospective cohort studies considering nutrition and maternal weight outcomes, in particular GWG, in general populations of women without specific health conditions
• a review of dietary patterns and GWG undertaken by the United States Department of Agriculture (USDA)

SACN assessed the methodological quality of the identified systematic reviews and meta-analyses using a measurement tool (‘AMSTAR 2’) and prioritised those that were better quality (with higher AMSTAR 2 ratings). The certainty of the identified evidence was assessed using ‘GRADE’ (grading of recommendations, assessment, development and evaluation). GRADE uses 4 levels to categorise evidence, which are:

• high (where there is very high confidence in the evidence considered)
• moderate (where there is moderate confidence in the evidence considered)
• low (where there is limited confidence in the evidence considered)
• very low (where there is very little confidence in the evidence considered)

Weight status and dietary intakes

Survey data of pregnant women (2018 to 2019) found that around half were living with overweight or obesity (50.3%) when they attended their first antenatal appointment. About 3% of pregnant women were living with underweight.

Recent national surveys in the UK show that overweight and obesity is common and increasing among non-pregnant women in the UK. In 2022, between about a third and two-thirds of women aged 16 to 54 years in England were living with overweight or obesity, with the prevalence increasing with age. In 2022, around 1 in 10 non-pregnant 16 to 24 year olds in England were underweight.

The highest rates of overweight and obesity are seen in the most deprived areas of the UK. The Health Survey for England 2022 and Scottish Health Survey 2022 found that over two-thirds of non-pregnant women (aged 16 years and over) in the most deprived areas were living with overweight, including obesity, compared to around half of women in the least deprived areas.

There is no national dietary data set available on pregnant or breastfeeding women in the UK. Dietary survey data indicates that, as for the UK population overall, most women of childbearing age are not meeting UK dietary recommendations, including for vegetables and fruit, fibre, oily fish, sugar, salt or saturated fat intake. Associated modelling indicates that their energy intakes are likely to exceed UK dietary recommendations.

Evidence from systematic reviews and meta-analyses

The evidence identified from systematic reviews is summarised below. The certainty of the evidence, assessed using GRADE, is in brackets. The included studies considered a broad range of dietary interventions and patterns. The dietary patterns are as they were defined by study authors. The information below was graded as high, moderate or low certainty. Evidence for other dietary factors and interventions was either graded as very low certainty or was not identified through systematic literature searches.

Pregnancy weight outcomes

Risk of excess GWG was higher for women who had an ‘unhealthy’ dietary pattern in pregnancy. This was characterised by diets high in refined grains, saturated fats, red meat, processed meat, fast foods, and high sugary foods and drinks (low certainty evidence).

Risk of excess GWG was lower for women who had a:

• ‘low glycaemic load’ dietary pattern in pregnancy (high certainty evidence) - this type of diet means choosing foods that raise blood sugar more slowly and over a longer time period, such as whole fruits, vegetables and nuts
• ‘healthier’ dietary pattern in pregnancy, which was defined as being higher in vegetables, fruits, nuts, legumes and fish and lower in added sugar, red and processed meat (USDA defined this evidence as ‘limited certainty’)

Average GWG was higher for women who had a higher energy intake in pregnancy (low certainty evidence).

Average GWG was lower for women who:

• had a ‘Mediterranean’ dietary pattern in pregnancy (moderate certainty evidence) - this tends to include higher intakes of vegetables, fruit, legumes, cereals, nuts, seeds, fish and monounsaturated fatty acids (for example, olive oil) and lower intakes of saturated fat, dairy products and meat
• had a ‘low glycaemic load’ dietary pattern in pregnancy (moderate certainty evidence)
• took part in dietary interventions in pregnancy (low to moderate certainty evidence)

There was no association between average GWG and an ‘unhealthy’ dietary pattern in pregnancy, which was characterised by refined grains, foods high in saturated fats, red meat, processed meat, fast foods, and high sugary foods and drinks (low certainty evidence).

There was no effect of probiotic supplements on average GWG in women who were living with overweight or obesity (high certainty evidence).

Postpartum weight outcomes

Dietary interventions in the postpartum period improved weight loss (moderate certainty evidence).

Weight retention in the postpartum period was reduced with a ‘low glycaemic load’ dietary pattern (low certainty evidence).

There was inconsistent evidence on weight retention and dietary interventions during pregnancy and/or in the postpartum period for women living with overweight or obesity (low certainty evidence).

Limitations

SACN identified a range of limitations in the evidence they considered.

There is no national dietary survey data on pregnant or breastfeeding women in the UK. The available data on women of childbearing age is self-reported. It may be affected by under or misreporting, which is common in all dietary surveys.

Most of the studies included in the systematic reviews and meta-analyses considered diet and physical activity together. Only a minority of studies considered diet alone.

It was difficult to apply GRADE to the type of evidence available on this topic. The evidence for some dietary factors was considered low or very low certainty.

The interventions included in systematic reviews and meta-analyses:

• rarely reported BMI measured at the start of pregnancy - studies tended to rely on self-reported measures and/or measures from the first trimester of pregnancy
• lacked trimester specific evidence
• used a broad range of methods making it hard to identify the most effective interventions
• rarely assessed how well participants followed the intervention they were asked to do
• tended to be short because most started in the second trimester of pregnancy (no studies started before pregnancy and few studies continued after birth)
• were unclear in how study findings were impacted by maternal BMI before pregnancy
• tended not to report on any adverse outcomes or negative experiences women may have had

Limitations in considering the evidence on GWG included:

• the lack of an agreed definition for appropriate or excess GWG
• many studies using average GWG - this meant it was unclear whether reported associations were due to an ‘appropriate’ or ‘inappropriate’ weight gain
• studies rarely assessing GWG by maternal weight at the start of pregnancy
• studies rarely considering population subgroups such as different ethnic, age or social groups
• general lack of evidence on adolescent girls

Conclusions

Weight status, energy intakes and requirements

A high and increasing number of women of childbearing age are living with overweight or obesity. SACN has previously highlighted the importance of beginning pregnancy at a healthy weight. This is also reflected in existing NHS advice. While excess or inadequate GWG can increase the risk of adverse health outcomes for the mother and baby, maternal BMI at the start of pregnancy is likely to be a relatively greater determinant of health outcomes for the mother and baby.

Intentional weight loss is not recommended during pregnancy because of potential adverse effects on the baby.

The evidence considered in this report tended to show that higher energy intakes during pregnancy were likely to be associated with excess GWG.

Existing advice is that women need around an extra 200 kcal a day in the last 3 months of pregnancy. In 2011, SACN noted that:

women entering pregnancy who are [living with] overweight [or obesity] may not require this increment but current data are insufficient to make a recommendation regarding this group.

Existing advice is that extra energy (around 330 kcal a day) is needed by women exclusively breastfeeding during the first 6 months after they have given birth. The recommended amount assumes that women will lose around 0.8kg each month after they have given birth. Breastfeeding (particularly exclusive breastfeeding in the first 6 months of a baby’s life) is associated with lower maternal BMI in the longer term.

SACN has not changed its advice on energy intakes for women during pregnancy or while exclusively breastfeeding. Evidence considered in this report indicated that women of childbearing age already had high energy intakes. So, usual energy intakes by women living with overweight or obesity may meet or exceed energy requirements during pregnancy or exclusive breastfeeding, and no further increase may be required. However, it is unclear whether there would be any unintended consequences of changing existing advice for these women.

Living with underweight is also a risk for the mother and baby. In 2011, SACN noted that women who were living with underweight at the beginning of pregnancy may have a higher energy requirement than other women.

There is no specific dietary advice for adolescent girls who become pregnant. Girls who have not stopped growing may have higher energy requirements during pregnancy than other women. However, the evidence is limited and the energy needs of girls during pregnancy and breastfeeding are not clearly understood. Underweight is more common in this age group. Overweight and obesity is also an issue among girls, though fewer are living with overweight and obesity than in older age groups.

Dietary patterns

Study authors use varying definitions of a healthy diet, but these generally align with existing UK recommendations. While some of the evidence identified on dietary patterns was of low or very low certainty, it generally indicated that improving diets during and after pregnancy has modest beneficial effects on GWG and weight after pregnancy. There is no evidence that a healthier diet during pregnancy was linked to any adverse effects.

Many women of childbearing age have poor dietary patterns and are not achieving UK dietary recommendations. Encouraging a healthier dietary pattern and achieving and maintaining a healthy weight is likely to be associated with a wide range of health benefits for all women, but especially those planning a pregnancy or who may become pregnant.

The current evidence does not support the use of dietary supplements, in relation to GWG, for most women.

Development of recommendations

This is the first report in which SACN has used GRADE to assess the certainty of the available evidence.

GRADE has benefits in giving additional transparency to SACN’s work. However, using GRADE for public health topics such as nutrition can be challenging. This was particularly the case for this report because most of the evidence is observational, which GRADE usually considers low certainty.

For this report, SACN agreed to make recommendations based on evidence assessed as low, moderate or high certainty, in line with the SACN framework.

Recommendations

The following recommendations are for government in relation to girls and women of childbearing age (aged 14 to 49 years) and pregnant or breastfeeding women. SACN has made these in the context of existing UK dietary advice, and they should be read alongside the NICE guidelines:

• Maternal and child nutrition: nutrition and weight management in pregnancy, and nutrition in children up to 5 years
• Overweight and obesity management

The full report also includes research recommendations to address the many evidence gaps identified.

Population subgroups

The needs of the following groups should be a particular focus when considering all the recommendations:

• vulnerable groups (such as adolescent girls and older mothers)
• racially and ethnically diverse groups
• people experiencing multiple disadvantage

When collecting data on body weight status, and nutrient intake and status, specific consideration should be given to study design to allow assessment of these population subgroups.

Existing UK dietary recommendations

SACN reiterates existing UK dietary recommendations for women of childbearing age. These include avoiding energy intakes that exceed requirements. Achieving and/or maintaining a healthy weight is a priority before pregnancy and between pregnancies.

Table 2.1 in the main report summarises current UK dietary reference values for energy and macronutrients for women of childbearing age (and the increases needed during pregnancy and breastfeeding).

Women who are pregnant or breastfeeding, and women of childbearing age, particularly those who are planning a pregnancy or who may become pregnant, should follow existing UK dietary recommendations.

SACN reiterates existing recommendations on energy requirements for women during pregnancy and breastfeeding made in the SACN Dietary reference values for energy report, which are that:

• 0.8 megajoules (MJ) a day (191 kcal a day) is added to a pregnant woman’s estimated average requirement (EAR) for energy during the last trimester (EAR is calculated using the woman’s weight before pregnancy)
• 1.38 MJ a day (330 kcal a day) is added to a mother’s EAR for energy in the first 6 months after giving birth for women who are exclusively breastfeeding (EAR is calculated using the woman’s weight before pregnancy)

Maternal weight gain and postpartum weight loss

For maternal weight gain during pregnancy and postpartum weight loss, SACN recommends:

• avoiding energy intakes that exceed requirements
• eating a healthy balanced diet in line with existing UK dietary recommendations
• exclusive breastfeeding for around the first 6 months of an infant’s life and continued breastfeeding into the second year of life and beyond

Recommendations for government to consider

SACN recommends that government considers:

• continuing to collect data on measured maternal body weight status nationally at the start of pregnancy and reporting this data by BMI category
• collecting detailed, nationally representative data on nutrient intakes and status of pregnant and breastfeeding women
• continuing to collect (through NDNS) detailed nationally representative data on nutrient intake and status of women of childbearing age
• focusing prevention activities on reducing prevalence of overweight and obesity before pregnancy, as this is where maternal and child health benefits are likely to be greatest
• strategies to support women of childbearing age to maintain or achieve a healthy BMI
• strategies to support women of childbearing age, particularly those planning a pregnancy, to eat a healthy balanced diet in line with UK dietary recommendations
• strategies to promote and support breastfeeding, particularly exclusive breastfeeding, for around the first 6 months