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How to Fuel Your First Trimester of Pregnancy as a Runner

Stay fit, happy, and healthy early in your pregnancy by feeding your body what it needs.

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Contrary to stereotypes about expectant women, pregnancy—particularly the first trimester—isn’t best served by a caloric free-for-all. Physiologically, your body has no need for extra calories during those first 12 weeks, although keep in mind that a woman active in endurance sports (or other activities) needs sufficient caloric replacement for what she’s burning. Because your ideal intake depends on the forms and duration of your exercise, talk to your doctor about your specific training and eating additional daily calories when you’re using energy through exercise.

When it comes to how and what you eat, aim to eat small meals every few hours during the day to avoid a drop in blood sugar, which is a risk in early pregnancy because of the major metabolic changes happening. Eating small, frequent meals also helps prevent nausea and dizziness, particularly an hour or so before a workout and right after you finish, when your blood sugar is likely to be low. As you’ve probably heard, you might have particular food cravings or turnoffs because of the wild ride your hormones are on.


Carbohydrates are essential to fueling your performance as an active woman. Carbs will also help to fuel the workout going on inside your body as a pregnant woman. You need energy to fuel the activity in your uterus and any activity you pursue for yourself, especially if you’re an endurance athlete. Your body is using more carbohydrates while you’re pregnant, which can lead to low blood sugar when exercising, so replacing carbs immediately after a workout is essential.

Because your body’s carbohydrate use corresponds to the level of exercise intensity, you’ll want to focus on replenishing your calories in the form of complex carbs, such as whole-grain pastas, quinoa, nuts, beans, and brown rice, because complex carbs offer more fiber that slows digestion. Avoid eating simple carbs (white bread, for example) as much as possible, and to aid digestion, try not to rush through eating meals in a short amount of time. While this can be hard if you’re working and need to eat quickly during a busy day, relying on quick meals of simple carbs prompts unnecessary weight gain because your body metabolizes the sugars in simple starches, such as pastries and muffins, so quickly that you will find yourself hungry again before you leave the table. Whole grains take longer for your body to break down, keeping you full and giving you and the baby nutrients in the process. As an added perk, fiber can also reduce the nausea of the first trimester. If you can eat several smaller meals with complex carbs, your energy will benefit, you’ll digest the food more easily, and you’ll be more likely to get a quality workout because you’ll burn the fuel more efficiently.

Doctor’s Note

If you get regular, vigorous exercise, you will need to replace 300 calories per day in the first trimester. Your caloric need will increase for the same level of exercise as you gain weight over the 40 weeks. You won’t need any increase in the first trimester other than replacing what you’ve burned, but the same kind of exercise demands more energy (and calories) when you’re heavier in the third trimester.


As an athletic woman, you should emphasize foods that serve as high-quality fuel for activities that burn a lot of calories. On top of complex carbs, you’ll want sufficient protein from meat and/or legumes. If you’re a vegetarian, you can get plenty of protein from beans and nuts. The difference between protein from plants and protein from animals is that animal proteins contain all of the essential amino acids, unlike plant proteins, which are incomplete. Because they consume more phytoestrogen, vegetarian women have an increased risk of hyposadias (a genital birth defect) in male babies. However, this condition is fairly rare, and a vegetarian can find quality nutrition in fortified soy products. In addition, vegetarian women will want to pay extra attention to boosting vitamin B12, iron, and vitamin D.

Eating seafood is fine; however, you need to limit the types and quantities of certain fish to avoid intake of too much mercury. According to the Environmental Protection Agency, too much mercury can pose a risk to the development of a baby’s nervous system. ACOG advises that you steer clear of shark, swordfish, king mackerel, or tilefish during pregnancy, as these fish are known to have abundant mercury levels; however, you can eat halibut, rainbow trout, wild shrimp (farm-raised have pesticides), salmon, canned light tuna, and catfish because the mercury content is much lower.

Doctor’s Note

Vegetarian diets may not provide adequate amounts of essential amino acids, iron, trace minerals, vitamin B12, vitamin D, calcium, or complex lipids for normal embryonic and fetal development. It is recommended that vegetarians who are pregnant or planning pregnancy consult a nutritionist. Minor dietary alterations can resolve these issues, and vegetarians can eat fortified soy products, increase their dairy and egg consumption, and make sure they are taking prenatal vitamins to achieve good nutrition.

Prenatal Vitamins

Ask any woman who’s been pregnant, and she’ll probably tell you that prenatal vitamins are like a gift from the gods. Usually prescribed by your OB, they help you feel as well as you can, and many women swear that prenatal vitamins are largely responsible for the great skin and hair that often comes with pregnancy. With that in mind, follow the dosage indications on the supplements you take. While the daily recommended intake (DRI) can be higher for some vitamins during pregnancy, high doses of certain vitamins, such as A and D, can do more harm than good to fetal development.

Your prenatal vitamins will give you the extra iron and folic acid you need because of increased blood volume and an increase in red blood cells. Folic acid (folate, a B vitamin) helps prevent neural birth defects, and prenatal multivitamins will usually provide the 400 mcg you need for the first 12 weeks, though fortified cereals are also high in folate.

You need extra iron during pregnancy because you’re producing more blood to support your baby, and your red blood cells need more iron to send oxygen to your organs and to the fetus. ACOG recommends that you take 27 mg of iron every day. You’ll likely find this in your multivitamins, but as an active woman, ask your doctor if you need iron in addition to the DRI found in your prenatal vitamin. Low iron can lead to anemia, which is a risk for women during pregnancy. Anemia jeopardizes the safety of your fitness routine because this condition is characterized by blood that isn’t transporting oxygen well throughout your body, which is of course important to a safe and healthy workout. Symptoms of anemia include dizziness, shortness of breath, fatigue, and low blood pressure. Be advised that iron supplements can trigger an upset stomach and/or constipation, which are also common symptoms of the first trimester that you won’t want to exacerbate. You can offset these side effects by gradually adding more fiber from fruits and whole grains as well as by drinking more water, which your active body needs anyway.

Here are some of the top sources of iron for pregnancy:

  • Pinto beans, ½ cup (5 mg iron)
  • Fortified cereals, 1 cup (3.5 mg iron)
  • Tofu, ½ cup (3.5 mg iron)
  • Pumpkin, squash, or sesame seeds, 1 oz. (3.5 mg iron)
  • Beef, 3 oz. (2 mg iron)
  • Turkey, 3 oz. (2 mg iron)
  • Artichoke, medium (1 mg iron)

Doctor’s Note

It’s best to take your iron with an acidic food, such as orange juice, which aids absorption. Don’t take iron with tea, which is known to inhibit absorption.


Hydration is one of the most important factors throughout a fit pregnancy, but it’s especially critical in early pregnancy, when your vascular system pumps less blood relative to the expanded capacity of your circulation system. Over time, your body sorts out the deficit of blood circulating, and your blood volume and cardiac output will respond with an increase of about 40 percent, but during that process, your body risks dehydration. Dehydration can prompt uterine contractions, so it is important to stay hydrated when exercising. Drinking 8 ounces of water before exercise and 8 ounces of liquid for every 20 to 30 minutes of exercise will keep you well hydrated.

There are two people participating in any workout, and you’ll need to take in enough salt and fluids for both of you. Drink water continually throughout the day as well as while you exercise, striving to drink eight 8-ounce glasses every day. The body’s heart rate tends to creep up as it gets dehydrated and will stay lower when you are properly hydrated, so drinking plenty of fluid is an easy way to prevent overexertion.

Monitor hydration by checking your urine to make sure it’s very clear and by weighing yourself before and after exercise. A loss of weight signifies a loss of fluid that needs to be consumed before you work out again, and 1 pound of weight loss equals 1 pint of fluid to replace. If you are dehydrated (dark yellow urine or loss of weight after a workout), don’t work out again without fully rehydrating and checking your urine color for clarity. If you work out in the morning, keep a bottle of water next to your bed to drink if you wake up during the night so you’ll start the day well hydrated and prepared for a great morning workout.

If you’re a coffee drinker, it’s okay to have your morning cup, but keep in mind that caffeine is a diuretic and also crosses the placenta. While your fetus won’t develop birth defects from caffeine, if you drink coffee or other caffeinated drinks while pregnant, your baby might be born with an attachment to caffeine and could go through the same cranky withdrawal that any coffee-loving adult would experience if giving it up. You might consider weaning yourself by diluting your full-caffeine coffee with decaffeinated, gradually replacing the caffeine with decaf altogether.

Doctor’s Note

Salted or electrolyte drinks help keep fluid in blood vessels. Remember, though, to consume these in moderation. It’s best to alternate between plain and electrolyte waters. Your fluid balance from an exercise session can be measured by weighing yourself before and after your workout. Any loss of weight is body fluid, and 1 pound of weight is equal to about 1 pint of fluid.

Adapted from Fit and Healthy Pregnancy by Dr. Kristina Pinto and Rachel Kramer, MD, with permission of VeloPress.