By Lisa Drayer, CNN

(CNN) -- When it comes to diets, there are many varieties from which to choose: weight loss, plans to lower cholesterol and manage diabetes, and foods to fuel endurance athletes. Now, there's a diet that claims it can boost a woman's chances of having a baby.

The diet was developed by Drs. Jorge Chavarro and Walter Willett, both of the Harvard School of Public Health, based on their extensive data analysis of the Nurses' Health Study, one of the largest and longest-running studies of women's health in America.

After reviewing the diets of more than 18,000 women who did not have a history of infertility but who were trying to get pregnant, they found that the quality of your diet, along with how active you are and whether you smoke, can stack the reproductive deck in your favor.

For those having trouble conceiving, "high-tech medicine isn't the only answer," Chavarro and Willett wrote in their book, "The Fertility Diet: Groundbreaking Research Reveals Natural Ways to Boost Ovulation and Improve Your Chances of Getting Pregnant."

What other experts say

Other experts say Chavarro and Willett's diet may be helpful to improve fertility for women with ovulatory disorders such as polycystic ovary syndrome, often called PCOS. "It is an overall healthy way of eating and can help women improve their intake of key nutrients for conception and pregnancy," said Vandana Sheth, registered dietitian nutritionist and spokeswoman for the Academy of Nutrition and Dietetics.

Dr. Marie Menke, assistant professor and director of the division of reproductive endocrinology and infertility at UPMC Magee-Womens Hospital, agreed: "If you are going to be searching for a fertility diet, this is a good place to start. Research shows an association between this dietary pattern and a reduced risk of infertility in some women."

Experts agree that the diet has positive attributes, but some question whether the real benefit comes from losing weight rather than the quality of one's diet.

Carrying excess pounds can affect egg quality, explained Dr. Amanda Kallen, assistant professor of obstetrics, gynecology and reproductive sciences at the Yale Fertility Center. Also, women who are overweight or obese are more likely to have imbalances in insulin levels, in testosterone levels and in levels of FSH and LSH, and these hormones drive the growth of follicles and ovulation, Kallen explained.

"There's definitely data to suggest that coming back to normal weight can help those problems and promote ovulation, but there is not enough data to conclude definitively that one diet helps more than another."

Martha McKittrick, a registered dietitian and PCOS expert, said, "I've had many women who lost weight and got pregnant. The question is, did they get pregnant because they lost weight, or because they followed the other recommendations from the fertility diet?

"If a woman is overweight and trying to conceive, I try to help them lose weight. That, to me, is number one," McKittrick said. "Losing 10% of your weight (or 20 pounds if you weigh 200) improves insulin sensitivity and helps women with PCOS ovulate."

But a woman with PCOS can be lean and still be insulin-resistant, which can interfere with ovulation -- in which case the diet quality becomes a more important factor, McKittrick explained. For these women, eating fewer processed carbs and more whole-grain carbs such as quinoa, farro and whole-wheat bread over white bread can result in a slower rise in blood sugar and a lower insulin production, which is favorable for fertility.

"It makes sense for a patient with PCOS to lower her intake of highly processed refined carbs. In some patients, [these] dietary modifications can increase the likelihood of spontaneous ovulation," said Dr. Alan B. Copperman, director of the division of reproductive endocrinology and infertility and vice chairman of the Department of Obstetrics, Gynecology and Reproductive Science at Mount Sinai Medical Center.

Chavarro and Willett's research reveals that eating more full-fat dairy foods instead of low-fat or fat-free dairy can improve chances of conception among women having trouble ovulating. This is due to the presence of specific hormones in milk fat. But consuming more calories from full-fat foods can get tricky if weight loss is part of one's pregnancy prescription.

"I am a fan of 2% or full fat dairy. It's better than skim or 1% if you are trying to get pregnant, and it keeps you feeling full longer," McKittrick said. But to keep calories in check, she recommends cutting out an ounce of meat or a third of a cup of starch elsewhere in your diet.

More than 'one' fertility diet

Experts say that even if fertility medications or procedures are in the conception cards, improving your diet can optimize your chances of conceiving. But studies suggest that diets other than the fertility diet may also be beneficial. In one study, researchers concluded that diligently following the Mediterranean diet may help increase the chances of a successful pregnancy and birth for women undergoing in vitro fertilization.

"There is evidence that supports that various dietary patterns support fertility goals; however, most patterns have components in common, such as being rich in fruits, vegetables, whole grains and seafood," said Lauren Manaker, an infertility and prenatal dietitian who counsels women and men who want to conceive. "Eating this way will likely not hinder chances of conception versus eating a diet that is common in the Western world, which is rich in refined carbs and processed foods and low in vegetables."

In another study published last month and co-authored by Chavarro, a "pro-fertility diet" that included high levels of folic acid, vitamin B12 and vitamin D, as well as dairy, soy and low-pesticide produce, had a more favorable outcome on fertility when followed in conjunction with assisted reproductive technologies, compared with the Mediterranean diet.

With the "pro-fertility diet," the more compliant a patient was, the better the result. But researchers did not see the same relationship when they evaluated women with different levels of compliance with the Mediterranean diet and their assisted reproductive technology outcomes, Manaker explained.

"This new study highlights that components that are not included in the Mediterranean diet, like focusing on low pesticide residue produce and including supplementation of specific vitamins, may be a better choice for those undergoing ART," Manaker said.

Keeping expectations in check

Although following fertility diet strategies can boost your chances of a baby bump, "it's not an automatic 'you do this and your live birth rate goes up 10%,' " Menke said. What's more, if you don't have an underlying ovulatory disorder, you may not get a lot of added benefit through diet.

Kallen points out that while there is a possibility of benefit from following the fertility diet for women with ovulatory infertility, the data supporting it is based on relationships (which don't prove cause and effect), as well as self-reported accounts of one's diet (which can be inaccurate). "The question is: If you follow this diet, will it treat or cure infertility? I don't think you can say that's the case," Kallen said.

Copperman noted, "If you follow this diet, it doesn't mean you're going to get pregnant, and if you cheat, it doesn't mean that you're not going to get pregnant. It was a lovely study, and it was a huge study; there are tons of women who recorded their information ... but even in the world of big data, it doesn't mean that we can draw specific and personalized conclusions from a study that wasn't designed to ask these questions."

Copperman is concerned that women may become overly adherent to a specific diet -- and unnecessarily blame their infertility on not following something stringently enough.

"People come in all the time ... after we put them on a low-carb diet ... and then they say, 'the reason I didn't ovulate is because I had a roll at dinner.' No, no! Biologically, that makes no sense," Copperman said.

If you decide to try lifestyle changes, your age should also be considered. "If a woman is 26 years old, [not ovulating] for the last three years after she started eating unhealthy in college and became 10 pounds heavier, then I might say, 'try this first; don't go straight to IVF.' But I'd be cautious to wait a year on a diet if a woman is 40 years old. That would make me a little bit worried," Menke said.

At the end of the day, experts agree that when it comes to conceiving, having something in a patient's control is meaningful.

"It's a question that comes up a lot: Is there anything I should be eating or doing to make this better?" Menke said. "If you are looking for something anyway, this might not be a bad place to start."

The fertility diet in 11 recommendations

Chavarro and Willett recommend in their book 10 research-based strategies that could potentially boost fertility:

1. Avoid trans fats, the artery-clogging fats found in many commercially prepared products and fast foods.

2. Use more unsaturated vegetable oils, such as olive oil or canola oil.

3. Eat more vegetable protein, like beans and nuts, and less animal protein.

4. Choose whole grains and other sources of carbohydrates that have lower, slower effects on blood sugar and insulin rather than highly refined carbohydrates that quickly boost blood sugar and insulin.

5. Drink a glass of whole milk or have a small dish of ice cream or full-fat yogurt every day; temporarily trade in skim milk and low- or no-fat dairy products like cottage cheese and frozen yogurt for their full-fat cousins.

6. Take a multivitamin that contains folic acid and other B vitamins.

7. Get plenty of iron from fruits, vegetables, beans and supplements, but not from red meat.

8. Beverages matter: Water is great; coffee, tea and alcohol are OK in moderation; stay away from sugared sodas.

9. Aim for a healthy weight. If you are overweight, losing between 5% and 10% of your weight can jump-start ovulation.

10. If you aren't physically active, start a daily exercise plan. If you already exercise, pick up the pace of your workouts. But don't overdo it, especially if you are quite lean. Too much exercise can work against conception.

11. If you smoke: stop.

Chavarro and Willett say the diet recommendations are specific to women with ovulation-related infertility and not infertility related to blocked fallopian tubes or low sperm production. Their book offers a week-long meal plan with recipes that are consistent with the above strategies and delivers approximately 2,000 calories per day.