Nutrition, Pregnancy, and Preexisting Diabetes: Exploring What Has Changed and What Remains the Same

Abstract

Nutrition is a key component in the management of pregnancy. If diabetes is also involved, the maternal physiological and hormonal changes can have a profound effect on glycemic levels. Eating habits, which include what and how foods are consumed, and even culture are other contributing factors that influence maternal and fetal outcomes. Most nutrition recommendations can be applied to all pregnancies; however, adjustments may be necessary if diabetes predated the pregnancy. This article provides an update, addressing both what has and has not changed in recent years in the nutrition management of pregnancy and preexisting diabetes.

Nutrition plays a crucial role in pregnancy. Physical changes intertwined with surging hormones and the demands on the body to carry a developing fetus for 40 weeks imposes life-altering mental and physical effects. Chronic conditions such as diabetes, when added into the equation, contribute additional concerns or burdens to pregnancy. However, it is possible to have a healthy pregnancy and healthy baby when careful planning and follow-up care are executed. There are certainly differences in care for pregnancies complicated by diabetes. Knowing what has changed and what remains the same in this scenario is helpful for practitioners as they implement nutrition and glycemic goals with their patients.

Referral to a registered dietitian nutritionist (RDN) who specializes in diabetes and pregnancy can be pivotal, in not only evaluating meal patterns, frequency of intake, and glycemic goals, but also assessing and determining carbohydrate-to-insulin ratios and macronutrient and micronutrient needs (Table 1). What has changed and what has remained the same regarding nutrition and diabetes pregnancy recommendations? Let’s start with macronutrients.

Table 1.

Minimum Amounts of Vitamins and Minerals Recommended in Pregnancy (15)

Vitamin/Mineral	Recommended Intake Per Day
Iron (elemental)	27 mg
Calcium	1,000–1,300 mg
Folate	0.4 mg in first trimester; 0.6 mg in second and third trimesters
Iodine	250 μg
Vitamin D	200–600 IU (maximum 4,000 IU)
Vitamin B6	1.9 mg
Magnesium	350 mg
Zinc	11 mg
Choline	450 mg
Selenium	60 μg
DHA	250–500 mg (maximum 1,000 mg)*

*Clinicians could consider prescribing 1,000 mg/day DHA during pregnancy to reduce early preterm birth in women with low DHA status if they are able to screen for DHA (16).

Macronutrients

Carbohydrates

The minimum amount of carbohydrates recommended for pregnant women is 175 g/day, which is 45 g more than the recommendation for nonpregnant adults. This recommended dietary reference intake (DRI) remains the same in pregnancy for individuals with preexisting diabetes or gestational diabetes mellitus (GDM). The 175 g carbohydrates is needed for maternal function and fetal growth (1).

The percentage of carbohydrates for pregnancy with preexisting diabetes may vary depending on which entity or organization is referenced. The American Diabetes Association (ADA) recommends 40–60% of the calories from carbohydrates, the American College of Obstetricians and Gynecologists (ACOG) recommends 40–50%, the American Association of Clinical Endocrinologists recommends 35–40%, and the Endocrine Society recommends 35–45% (2–4).

It is important to note that restricting carbohydrates and replacing them with an increase in dietary fat consumption may result in fetal overgrowth (5).

Fat

The DRI for fat in pregnancy (20–35% of calories) is similar to the general population (1). Recommended types of dietary fats are predominately monounsaturated and polyunsaturated, with an emphasis on limiting the intake of trans and saturated fats. The American Heart Association recommends consuming <6% of calories from saturated fats (5); the 2020–2025 Dietary Guidelines for Americans recommends <10% of calories from saturated fats (6). Excess dietary fat intake can lead to insulin resistance because of increased free fatty acid levels, which are known to negatively affect insulin sensitivity, thereby increasing glucose production in the liver (7). Although there are limited studies that address fat intake in pregnancy with preexisting diabetes, one GDM study found that diets high in fat increased free fatty acid levels, which may increase insulin resistance (8). Clinicians should consider prescribing 1,000 mg of docosahexaenoic acid (DHA) daily during pregnancy to possibly reduce early preterm birth in women with low DHA levels (9).

Protein

There are no current recommendations for protein intake for pregnant women with preexisting diabetes. The Acceptable Macronutrients Distribution range for protein is 10–35%. The Recommended Daily Allowance in pregnancy is 1.1 g/kg/day during the second and third trimester and is calculated for singleton pregnancies using the pre-pregnancy weight. Additional protein is required in the second and third trimester for women carrying multiples, calculated by adding 50 g protein daily to the nonpregnant DRI of 0.8 g/kg/day (10).

Energy

Energy or calorie requirements during pregnancy are the same for people with or without diabetes. Currently recommended energy requirements during pregnancy are shown in Table 2.

Table 2.

Energy Requirements During Pregnancy (1,9)

Trimester	Estimated Energy Requirements
First	Same as for nonpregnant adults
Second	Requirement for nonpregnant adults +340 kcal
Third	Requirement for nonpregnant adults +452 kcal

Order of Eating Nutrients

There has been increased attention given to the order in which food is eaten as new research emerges. For many years, it was understood that the amount and types of carbohydrates, and timing at meals (how frequently and how far apart meals and snacks should be eaten), affected glycemic outcomes. However, more recent research has suggested that eating fibrous vegetables and protein 10 minutes before other carbohydrates can help to increase time in the target glycemic range and reduce glycemic variability (11). Although this study was conducted in people with GDM, the order of eating (i.e., fibrous vegetables first, followed by protein next, and other carbohydrates last) could also be applied to women with preexisting diabetes. The order of food consumed during pregnancy should be given closer attention because it may influence glycemic outcomes. This is a strategy RDNs can recommend for preventing and managing hyperglycemia and glucose variability during pregnancy.

Resistant Starch

Consumption of resistant starch has emerged as a new method of managing glycemia. Resistant starch is a type of dietary fiber that is digested in the small intestine. There are five types of resistant starch; some are found in legumes, seeds, breads, and potatoes, and others are found in foods that have been cooked and cooled, such as oatmeal, rice, and pasta. Resistant starch not only aids carbohydrate and lipid metabolism, it also improves the gut microbiome by working as a prebiotic to feed the beneficial microbes in the colon (12).

Research has shown that resistant starch helps to reduce blood glucose excursions after meals, depending on the amount and type of resistant starch consumed and the individual (13). The blood glucose–lowering effect of resistant starch also has a second-meal effect; it continues to help regulate insulin activity into the next meal (14). Resistant starch may play a role in glycemic control by altering the gut microbiome in women with GDM, and this affect may also be applicable to pregnant women with preexisting diabetes (15).

Micronutrients

Minimum amounts of select vitamins and minerals recommended in pregnancy are shown in Table 1.

Micronutrients of Concern: Iodine, Vitamin D, Folate, and Vitamin B12

Iodine

Research has shown that iodine and glucose metabolism are closely connected (16). Thyroid disease and type 2 diabetes are two common endocrinology disorders often seen together in clinical practice. Although hypoglycemia may be related to hypothyroidism and hyperthyroidism to glucose intolerance, it is uncertain whether a direct association exists between iodine and glucose metabolism (17). In pregnancy, it is crucial that iodine levels are optimized because of an increased risk of fetal cognitive and developmental delay (18). A higher prevalence of preeclampsia is seen in pregnant women with mild to moderate iodine deficiency, and there is an increased risk of developing GDM in iodine-deficient pregnant women (18,19). The current recommendation for iodine in pregnancy, with or without diabetes, is 250 μg/day, which is found in most prenatal vitamin-mineral supplements (20).

Vitamin D

Vitamin D plays an important role in supporting material and fetal health with regard to hormone regulation, immune system function, and calcium absorption (21). Studies have demonstrated that low maternal vitamin D levels are associated with higher occurrences of preeclampsia (21,22). Very few studies have focused on preexisting diabetes, vitamin D, and preeclampsia. One study showed that pregnant women with diabetes are four times more likely to develop preeclampsia than women without diabetes (23). Another study comparing vitamin D–deficient women with type 1 diabetes versus a control group showed that the women with type 1 diabetes had higher A1C levels and a higher prevalence of preeclampsia than those in the control group (24).

Vitamin D supplementation of >400 IU/day is recommended during the third trimester to reduce the risk of neonatal and fetal mortality. A meta-analysis of randomized controlled trials (RCTs) revealed that supplementation of vitamin D in pregnancy can lower the risk of preeclampsia, thereby lowering the risk of fetal or neonatal death (25).

Vitamin D deficiency has also been linked to insulin resistance (24,26). Low vitamin D levels are common in pregnancy and have been found in GDM. One study noted a higher prevalence of severe vitamin D deficiency in GDM compared with normoglycemic pregnancies (24). Another study indicated low vitamin D levels in GDM and an increased risk of adverse maternal and offspring health outcomes (27). However, there is limited research on adverse outcomes of vitamin D deficiency in pregnancy with preexisting diabetes.

The Endocrine Society recommends that providers not routinely check for vitamin D deficiency in pregnant women, but rather consider empiric vitamin D supplementation, including daily intake of fortified foods, a prenatal vitamin-mineral supplement containing vitamin D, and/or a separate vitamin D supplement (28). According to ACOG, there is insufficient evidence to support screening all pregnant women for vitamin D deficiency; however, it suggests that women thought to be at risk (e.g., vegetarians, individuals with limited sun exposure, and those from racial/ethnic minority groups, especially those with darker skin) should be considered for screening (29).

Folate and vitamin B12

B vitamins such as folate and vitamin B12 play an integral role in blood glucose regulation. Low B12 and high folate levels are associated with insulin resistance and may increase the risk of developing GDM (30). Although the majority of studies have found that low vitamin B12 and high folate increases the risk of GDM, limited studies are available to assess whether insulin resistance is the same in GDM as in preexisting diabetes (16).

Prenatal Vitamin-Mineral Supplementation

Obtaining nutrients through food is of great importance; however, many women cannot consume adequate amounts of nutrients through diet alone. Because of the many metabolic processes taking place during pregnancy, there is an increased need for vitamin and mineral supplementation, without which many minerals can decrease markedly. Besides folate, vitamin B12, and vitamin D, other minerals at risk for deficiency may include magnesium, calcium, iron, selenium, zinc, and chromium (31).

Checking for Micronutrient Deficiencies as They Relate to Glucose Management

Understanding how key nutrients (e.g., iodine and vitamin D) affect glucose metabolism is imperative throughout pregnancy for the diabetes care team and particularly RDNs working with pregnant individuals. What has changed in how RDNs contribute to the care of pregnant women with diabetes? The need to monitor and evaluate specific vitamins and minerals as they relate to insulin resistance or glucose metabolism has changed based on new and emerging research. RDNs should assess and evaluate specific micronutrients through laboratory testing, if applicable, to ensure adequate meal intake and the need for vitamin and mineral supplementation. An individualized approach to micronutrient monitoring is suggested based on each woman’s health profile.

Fluid Needs in Pregnancy

Dehydration in diabetes can lead to hyperglycemia and ultimately diabetic ketoacidosis, if not treated promptly. Insufficient fluid intake in pregnancy is associated with urinary tract infections, constipation, low amniotic fluid levels, and premature birth. Although there is no definitive minimum daily fluid intake in pregnancy, ACOG recommends at least 8–12 glasses of fluids daily. There is no separate recommendation for women with preexisting diabetes (32). The type of liquids consumed is also important. In a committee opinion, ACOG suggests limiting maternal caffeine consumption to <200 mg/day (33).

Nutritive and Nonnutritive Sweeteners: What’s New?

Nutritive sweeteners include, but are not limited to, sugars (e.g., sucrose, fructose, glucose, lactose, and maltose), honey, maple syrup, and sugar alcohols. These sweeteners contain calories, and their intakes should be limited (2). People with diabetes, including pregnant women, often aim to reduce added sugar by choosing foods or drinks with sugar alcohols, which can be a way to mitigate the sharp elevation in blood glucose. Erythritol is a sugar alcohol nutritive sweetener that was associated with cardiac events in more than 1,000 people tested over 3 years (34). Still, erythritol is not required to be listed on nutrition facts labels of packaged foods. It can be found in sugar-sweetened beverages, and studies show that after consuming these drinks, platelet counts increased significantly even several days after consumption, increasing the risk of cardiovascular events (34,35). Since the study by Witkowski et al. (35) showed only an association and not a causal link, the U.S. Food and Drug Administration (FDA) has recommended additional studies to help clarify whether circulating erythritol levels are pathogenic (36). The FDA designates sugar alcohols as generally recognized as safe for consumption in pregnancy. RDNs should share the available information on erythritol with their pregnant patients so informed decisions can be made on its consumption.

Nonnutritive sweeteners contain zero calories and are categorized as plant-based (e.g., stevia, luo han guo [monk fruit extract], and thaumatin) or artificial (e.g., saccharin, aspartame, sucralose, acesulfame potassium, neotame, and advantame). According to a study on transplacental transport of artificial sweeteners, “. . . acesulfame, cyclamate, saccharin, and sucralose readily cross the placental barrier and enter the fetal circulation, and . . . these artificial sweeteners are present in the amniotic fluid” (37). For this reason, RDNs should share this information with their pregnant patients.

Eating Patterns

Any eating plan that severely restricts any macronutrient should be avoided. This includes low-fat and low-carbohydrate plans. The ADA recommends an eating plan that includes whole fruits, vegetables, whole grains, legumes, lean protein, and healthy fats, including nuts and seeds. Processed foods, fatty red meats, and sweetened foods and beverages should be limited (2). A list of eating patterns can be found in the ADA’s 2019 nutrition consensus report (38).

Weight Gain

Currently, there are no specific weight gain recommendations for diabetes in pregnancy. Since 2008, the Institute of Medicine (IOM) guidelines have recommended avoiding excessive weight gain without compromising maternal and fetal outcomes (39). The total amount of weight gain is dependent on the pre-pregnancy BMI. The IOM weight gain guidelines are shown in Table 3.

Table 3.

Gestational Weight Gain Guidelines (39)

Weight-for-Height Category	Recommended Total Weight Gain for Singleton Gestation, lb (kg)	Weekly Weight Gain Rate in Second and Third Trimesters for Singleton Gestation, lb (kg)	Recommended Total Weight Gain for Twin Gestation, lb (kg)
Underweight (BMI <18.5 kg/m2)	28–40 (7–18.2)	1 (0.5)	Not available
Normal weight (BMI 18.5–24.9 kg/m2)	25–35 (6.8–11.3)	1 (0.5)	37–54 (16.8–24.5)
Overweight (BMI 25.0–29.9 kg/m2)	15–25 (6.8–11.3)	0.66 (0.3)	31–50 (14.1–22.7)
Obese (BMI ≥30 kg/m2)	11–20 (4.5–9.0)	0.5 (4.5–9.0)	25–42 (11.3–19.1)

While the weight gain recommendations remain controversial for the above-normal BMI category, ACOG’s Committee on Obstetric Practice recommends individualized care and clinical judgment for those in the overweight and obese categories, who may want to gain less weight during pregnancy than the IOM guidelines suggest (40).

Herbal and Dietary Supplements

Although the use of herbal products in pregnancy may be widespread, little is known about their effects on fetuses. Herbals can be in the form of pills, powders, or tinctures, and the amount ingested varies. Dietary supplements such as protein powders, garlic tablets, or energy drinks that are consumed preconception could be continued during pregnancy, without any thought given to their possible teratogenicity. Ginger and vitamin B6 are commonly used to manage nausea and/or vomiting. Some herbal teas, such as peppermint or chamomile, have also been used with mild gastrointestinal discomfort. However, most herbal products are contraindicated during pregnancy. More information on herbal supplements during pregnancy can be found in the Natural Medicines Comprehensive Database (41). Health care providers must be informed about all supplements, including over-the-counter products, used during pregnancy. There are no separate recommendations for women with preexisting diabetes.

Functional Foods and Beverages

When we think of functional foods and beverages, apple cider vinegar (ACV) definitely stands out. The potential benefits of ACV have gone from mainstream media descriptions to scientific research. Apples that have been fermented past the alcohol stage leads to the formation of acetic acid. Acetic acid is responsible for the delayed digestion or gastric emptying of carbohydrates, leading to a slow rise in blood glucose levels.

A recent RCT revealed that daily intake of 30 mL of ACV not only significantly lowered postprandial blood glucose and A1C, but also improved the lipid profile in people with type 2 diabetes (42). Another study found positive effects on glycemia, including fasting blood glucose, and a reduction in oxidative stress in people with diabetes who consumed 20 mL/day of ACV for 8 weeks (43). Another study reported that 10–30 mL (2–6 tsp) taken after a carbohydrate-rich meal improved glycemia (44).

There are limited studies available on ACV use in pregnancy, especially among those with preexisting diabetes. Unpasteurized ACV contains the “mother” (i.e., the probiotic content or microbes) from the fermentation process, which may pose a concern for pregnant women. As with any other unpasteurized products such as raw milk or raw cheese, unpasteurized ACV should not be used during pregnancy because of the risk of infection (e.g., listeria). If taken, ACV must be diluted; some recommend diluting 1–2 Tbsp in 8 oz of water.

Research studies conducted on ACV show that it improves insulin sensitivity and postprandial glucose. ACV also may be helpful in reducing reflux, something pregnant women would appreciate, and even may reduce yeast infections, although research is needed to validate these outcomes.

Cultural Considerations

Understanding cultural influences is an important construct in health care, and that includes diabetes management. Because diabetes is primarily self-managed, health care providers must consider how nonmedical factors such as individuals’ culture affect well-being. Health care providers are not expected to know every person’s cultural nuances. However, achieving cultural competence, which is defined as “the integration and transformation of knowledge about individuals and groups of people into specific standards, policies, practices, and attitudes used in appropriate cultural settings to increase the quality of services, thereby producing better outcomes,” will certainly help individuals to achieve their health care goals (45).

Practicing cultural humility, which involves a willingness to learn about others from different cultures, allows health care providers to incorporate patients’ values and beliefs into a diabetes management plan, thereby fostering a more positive experience and better adherence. This strategy is especially important for medical nutrition therapy, through which dietary changes that are contrary to cultural customs could present challenges to following a nutrition prescription. Food is not only essential, but also personal. Health care providers who understand the cultural significance of food will be able to deliver more effective nutrition plans.

Resistant starch is one example of the intersection of culture and food. Many cultural foods from all over the world, such as yellow yams, maize, cassava, green bananas, and breadfruit, possess characteristics of resistant starch that can aid in blood glucose regulation. Some patients with diabetes may mistakenly believe that some of their cultural foods are off-limits. RDNs should recommend culturally appropriate resistant starches, which may improve nutrition adherence, increase trust in health care providers, and yield better glycemic outcomes.

Conclusion

Managing pregnancy complicated by diabetes should ideally begin before conception. Nutrition is a key component in the management of diabetes and pregnancy, and patients who are planning a pregnancy or are currently pregnant should be referred to an RDN who specializes in this area. Exciting research is emerging on topics such as the most beneficial order in which to eat foods and the benefits of resistant starch, and the importance of culture and food also continues to gain attention. Although most nutrition recommendations for pregnancy and diabetes are the same as for individuals without diabetes, it is imperative that factors that affect glycemic control are incorporated into the pregnancy nutrition plan to improve maternal and fetal outcomes.

Duality of Interest

No potential conflicts of interest relevant to this article were reported.

Author Contributions

Both authors researched the data and wrote, reviewed, and edited the manuscript. S.-E.A.-H. is the guarantor of this work and, as such, had full access to all materials and takes responsibility for the accuracy and integrity of the content.