One in eight couples has difficulty getting pregnant or carrying a baby to term, leading more than 11 percent of women in the United States to use fertility services.
In my private nutrition practice, I'm seeing more and more clients in their 30s and 40s who are trying to get pregnant and want to make sure their eating habits help their chances of conception and support a healthy pregnancy.
Most of what we know about the effect of nutrition on fertility is courtesy of a study based on data from the landmark Nurses' Health Study.
The "fertility diet" study followed nearly 18,000 women who were trying to conceive, and tracked their nutrition and lifestyle habits over eight years. Participants followed a diet including plenty of plant-based foods such as vegetables, fruit, whole grains and beans, as well as protein-rich foods, healthy fats and a bit of full-fat dairy.
The researchers observed that a specific eating pattern was linked to having a 66 percent lower risk of ovulatory infertility and a 27 percent lower risk of infertility from other causes.
While this study doesn't show cause and effect, it does provide us with some valuable insights into nutrition and fertility.
A healthy weight
If you're over- or underweight, getting to a healthy weight range is one of the most important steps you can take to boost your fertility.
There appears to be a "fertility zone" for weight. To get your BMI, or body mass index, visit the National Institutes of Health website and use its BMI calculator.
If you're overweight, losing 5 to 10 percent of that weight can positively affect fertility. About 75 percent of overweight women who struggle with fertility have polycystic ovary syndrome, so it's important to get checked by your doctor to have any health issues resolved and/or managed.
This emphasis on weight doesn't mean it's time to crash diet. Food scarcity (aka dieting) negatively influences your fertility. It makes sense from a biological perspective: Your body needs to know the food supply is reliable and nutritious before bringing a baby on board.
A recent systematic review found that a balanced eating plan that promotes gradual weight loss is better for fertility than drastically cutting calories.
Men also need to follow a healthy eating plan and get to a healthy weight to boost fertility. Being overweight can have a negative impact on testosterone levels, sperm count and motility.
There has been some headline-grabbing buzz that low-carb diets increase fertility. A recent review of low-carb diets and fertility found that of the interventions that have been done, the definition of a low-carb diet varies greatly and often is combined with other interventions.
As a result, we don't know enough about the effect of these diets to recommend them during the preconception period.
Further, overdoing it on animal protein probably isn't helpful. The "fertility diet" study found that ovulatory infertility was almost 40 percent more likely in women who ate the most animal protein.
According to Hillary Wright, a dietitian and director of nutritional counseling for the Domar Center for Mind/Body Health at Boston IVF, "The body uses nutrients in plant-based foods to neutralize the effects of toxic exposure, inflammation and more, so it makes sense to emphasize these foods during preconception and beyond."
The researchers looking at the fertility diet found that the more women ate fast-absorbing carbs such as white bread, white rice, potatoes, soda and candy, the higher their risk for ovulatory infertility.
They also observed that eating slow-absorbing carbs such as vegetables, whole grains, beans and lentils can provide a fertility boost.
As an added bonus, a high-fiber diet reduces the risk of gestational diabetes.
Wright advises clients to get their carbohydrates from whole foods and to spread them throughout the day in smaller portions.
She recommends making half your plate at each meal non-starchy vegetables, a quarter protein-rich foods and a quarter fiber-rich carbohydrates with some healthy fat.
Getting more vegetables, legumes, whole grains, fruit, nuts and seeds means more fiber and phytochemicals in your diet, helping to manage weight, improve health and boost fertility.
Taking in plenty of antioxidants from produce also seems to be beneficial for male fertility.
Add full-fat dairy
In the "fertility diet" study, consuming one to two servings of full-fat dairy products a day was linked to increased fertility, while low-fat versions showed the opposite trend.
It seems that having some whole milk or higher-fat yogurt could positively affect ovulation and conception, because the cream component of milk influences its balance of sex hormones.
Before you start putting cheese on everything and finishing every meal with a bowl of ice cream, note that it's one or two servings a day, and it's best to choose nutrient-rich options.
Wright advises her clients to use their saturated fat "budget" wisely. If you're going to have some higher-fat yogurt, put skim milk in your oatmeal.
You also don't want to get your fat from processed foods, as hydrogenated oils negatively impact fertility.
Although the Food and Drug Administration has banned the use of artificial trans fats in processed foods, this doesn't come into effect until June 2018.
Until then, read your ingredients lists and limit anything that has partially hydrogenated oils. Better yet, eat whole foods rather than packaged ones.
That's great advice for anyone to follow.
• Brissette is a dietitian, foodie and president of 80TwentyNutrition.com.