When clinical or behavioral evidence predicts an energy deficit as a possible dysregulator of fertility , the intervention of a nutrition professional could be important [1]. If this happens, the first step is to verify that the athlete’s energy intake is not sufficient by itself or in relation to the needs caused by training. Establishing this relationship is not a simple task. The use of reported energy intake (REI) as a predictor of caloric deficit requires a valid and accurate measure. A valid REI accurately reflects the energy that the athlete might have ingested over a period of time. A precise REI is a measure close to reality that is obtained from repeated determinations (e.g., a reported mean energy intake of 3500 kcal observed in an athlete using three 24-h recordings of food and drink intake is considered as valid and precise, when a 7-day-diet questionnaire with weight method for food and drink shows a mean intake of 3554 kcal/day for the same athlete).

In addition, it is recommended to evaluate the number of meals that the athlete ingests throughout the day. The portion size of the main foods with highly energetic nutrients (e.g., carbohydrates and fats) should also be determined with the help of visual materials such as photographs and scale models.

Subjects with a large volume and/or intensity of training could be subjected to energy demands that are difficult to satisfy in terms of food and meals . Furthermore, unlike exercise performed for a short duration at high intensity, appetite suppression often occurs at the end of a long-duration exercise at low or moderate intensity. For these reasons, the following dietary/behavioral strategies should be especially taken into account:

As stated earlier, the first step in correcting specific nutritional deficiencies that can affect fertility of an athlete is to ensure adequate global energy intake. Moreover, adequate intake of antioxidants and minerals is needed because of the importance of these nutrients.

It is also interesting to note that different dietary patterns have proven to be effective in improving oxidative and inflammatory status in healthy subjects or subjects with different chronic diseases such as obesity, diabetes, metabolic syndrome (MetS) , etc. [7−9]. Although most of the previously published studies have examined the effect of an increase in the availability of antioxidants on cellular phenomena associated with metabolic and cardiovascular risk , there is now sufficient evidence to show improved fertility through antioxidant nutritional therapy [10, 11].

Specifically, the Mediterranean diet has emerged as a dietary pattern with significant effect on the oxidative status in healthy individuals of different age groups [12, 13]. It is a dietary pattern characterized by abundant intake of minor components with antioxidants derived from varied and moderate consumption of fruits, vegetables, extra-virgin olive oil, and red wine.

From other cultural, or recent nutritional habits, dietary patterns and other foods have been proposed as they include high-antioxidant-potential compounds. Nutrients, such as honey, curcumin, omega-3 acids, or trans-resveratrol, could be included as examples among this type of substances.

It has been reported that honey has a protective role against oxidative stress produced during intensive training cycle, reducing markers of inflammation and oxidative stress and increasing levels of endogenous antioxidant systems [14, 15].

Meanwhile, curcumin present in curry, either alone or as an adjuvant with vitamin E, protects seminal glands, as well as sperm and testicular tissue, against toxic damage [16−18]. However, more research is needed about the effect of curcumin, as some studies have reported that, at least in animal models, curcumin could alter the onset of puberty in female mice as well as sperm quality and rate of live births in mice because of estrogenic/antiandrogenic activity and disruption of pregnancy [19].

Polyphenolic antioxidant compounds derived from grapes (especially proanthocyanidins), as in the case of resveratrol, are also common in Mediterranean diet (wine, grapes, peanuts, etc). In recent years, due to reported beneficial effects, it has drawn much interest among scientists having assessed its anti-inflammatory, antiviral [20], and antitumoral [21] properties and its potential effect on cardiopathies [22].

Although, strictly speaking, omega-3 fatty acids are not antioxidants, they are important components in many diets and seem to exert antioxidant-like properties, increasing total antioxidant capacity and decreasing inflammation and oxidative stress in tissues. Diets rich in fish are high in omega-3, which has been reported to increase both the male and female reproductive potential [23−25]. In females, omega-3 seems to improve folliculogenesis and oocyte quality as well as the prognosis in assisted reproductive technique (ART) procedures [24]. Moreover, there is evidence that these compounds help improve placental function by decreasing oxidative stress and inflammation [25]. In males, some studies have reported improved morphology and even a positive effect on oligoasthenoteratozoospermia [26].

In more western-style diets, walnuts can provide the benefits observed when consuming fish as they are also omega-3-rich fruits [27]. However, it seems that there is an altered relationship between omega-3 and omega-6 acids, similar to that of elevated linoleic acid (LA) omega-6/alpha linoleic acid (ALA) omega-3 ratio, which may affect female reproductive physiology, due to alterations in progesterone production, ovulation rate, and/or oocyte quality [28]. Moreover, the same authors have observed an identical effect in rat sperm , where an altered LA omega-6/ALA omega-3 ratio affects sperm density and motility. Mouse plasma progesterone levels are affected by different dietary omega-6/omega-3 ratios [28].

We could also highlight the Okinawan diet, which is a traditional Japanese dietary pattern that could be comparable to the Mediterranean diet and is characterized by a low calorie intake but rich in vegetables and fruits with reduced intake of meat, refined grains, saturated fat, sugar, salt, and full-fat dairy products [29]. Because of these characteristics, this is a phytonutrient and antioxidant-rich diet.

Obviously, an athlete with his/her own cultural characteristics and high energy demands as a result of his/her own sports practice (e.g., mainly carbohydrates in long-distance runners and proteins in the case of bodybuilders) may not meet all his/her dietary characteristics that define these dietary patterns and its healthy antioxidants. However, it would be desirable to adopt common strategies and habits to those dietary patterns that have proven to have increased daily intake of vitamins C and E, selenium, beta-carotene, and flavonols, including quercetin. These compounds have recently been associated with a significant improvement in fertility, especially leading to increased sperm count and mobility. The main dietary measures to enhance oxidative status according to current scientific evidence are:

MetS and obesity and polycystic ovary syndrome (PCOS) are pathologies that frequently involve fertility problems. Although many metabolic abnormalities, with possible implications on fertility (e.g., hypertension, insulin resistance, inflammation, and oxidative stress) , may be present in obese or MetS or PCOS subjects, there are two common components that worsen these alterations: excess weight and physical inactivity.

Obesity and MetS have been linked, both in men and women, to lower fertility rates and worsen the prognosis in ARTs [30−33]. Recognizing and treating patients with obesity, and especially those with associated MetS, can help improve not only fertility but also sexual and overall health [34].

Obesity has been associated with poorer sperm quality, oocyte quality, and embryo development. In men, poor sperm quality has been revealed by reduced sperm binding to hyaluronan-coated slides in men with high body mass index (BMI) and other unhealthy lifestyles such as smoking [35]. Moreover, in patients with MetS, it was observed that varicocelectomy improved semen quality, yet this improvement was not as effective as in patients without MetS. This seems to indicate that MetS can be a factor for male infertility [36]. The importance of obesity and MetS seems evident from a number of interventional studies showing that treatment with diet either alone or in conjunction with an exercise regime improves fertility [37]. However, with regard to surgical approaches to reduce obesity (bariatric surgery), there is no clear consensus as to whether this intervention helps in improving the fertility potential as evidenced by contradictory results from different studies [38−41]. These conflicting results may arise from confounding factors that were not taken into account in these studies. Therefore, it must be noted that careful patient selection and accurate clarification of their infertility cause and other health issues that may be present along with their obesity state are needed for obtaining proper knowledge.

In women, obesity has been found to affect mitochondrial metabolic function and increase mitochondrial reactive oxygen species (ROS) production, altering the initial stages of embryonic development [31]. Mitochondria are critical components in oocyte quality and embryo development as evidenced by studies revealing that defective mitochondrial biogenesis along with insufficient mitochondrial mass leads to failed oocyte maturation and hampered embryo development [42, 43]. Therefore, mitochondrial quality and quantity are required for successful fertilization and embryo development [31, 44].

Overweight and obesity were related to lower live birth rates in women undergoing ART treatment. In these cases, short-term weight loss intervention was related to higher metaphase II (MII) oocyte (mature) yield but not to clinical outcomes [45]. Other studies have also proven the efficacy of short-term nutritional and exercise intervention in increasing pregnancy rates [46, 47].

PCOS is a common complex, heterogeneous disorder that affects 5–10 % of women, normally appears in adolescence, and is one of main causes of female subfertility/infertility. In this condition, the ovaries contain many cystic follicles that are associated with chronic anovulation and overproduction of androgens. Symptoms may include anovulation , irregular menstrual periods, obesity, excessive growth of central body hair (hirsutism), and infertility. It can be associated with other systemic disorders, being commonly linked to MetS and obesity (obesity in up to 60 % of PCOS subjects depending on country), thus having a severe impact on quality of life [48].

Although PCOS is commonly treated with pharmacologic agents such as clomiphene citrate, due to the fact that this disorder is frequently associated with obesity and/or MetS , the recommendations that can be given with regard to nutrition and exercise are common. The changing of lifestyles is a key pillar in the treatment to improve the reproductive capacity of these individuals, requiring even the intervention on the psychological status of these patients to promote adherence to lifestyle changes. Thus, the two main lines of treatment are modifications leading to the acquisition of healthy nutritional habits and a more active lifestyle.

In order to improve the fertility potential of subjects with the above-mentioned pathologies, reducing body weight could allow for attenuating the negative effects associated with these pathologies [49]. It has been shown that weight reduction leads to increased fertility in women with obesity, MetS , and PCOS. Controlling obesity with dietary intervention is one of the main strategies used to promote weight loss.

Different nutritional strategies with caloric restriction have been proposed for long-term sustained weight loss and improvement of these conditions: short-term hypocaloric diet in women with PCOS led to a significant weight loss and a significant improvement in reproductive and metabolic abnormalities [50]; a low-carbohydrate, high-protein diet in in vitro fertilization (IVF) patients led to increased blastocyst formation rate and clinical pregnancy rate [51]. Although nutritional strategies alone seem to favor reproductive outcomes [52], it is suggested that diet and lifestyle interventions be implemented as a combined approach for subfertility in overweight and obese men.

However, one must be careful as extreme rapid dieting and acute very-low-calorie diets have been associated with poor natural reproductive and ART outcomes. Therefore, this type of patients should be offered the necessary advice and support for the needed weight loss and compliance to the dietary strategies (Table 20.2). When dealing with these patients, one should have a well-structured, realistic approach to a weight loss of approximately 5–10 % of initial weight. Moreover, structuring phases favors adherence to the program and prevents loss of motivation. In PCOS , weight loss of 5 % or greater will help in correcting ovulatory dysfunction or in reducing the dose needed for ovulation-inducing drugs [57].

Moreover, new theories, based on increasing dietary protein at the expense of carbohydrates, are gaining popularity for the treatment of obesity and PCOS [10, 51, 58]. Increased protein intake seems to facilitate short-term weight reduction (e.g., Zone diet), moderately reducing triglycerides levels and improving insulin sensitivity [59]. However, future studies are needed to determine the long-term maintenance of results achieved with these diets and their effect on the embryos at the different stages.

Most likely, the most adequate strategy would be to combine adequate nutrition with a carefully planned exercise intervention. Supplementation of antioxidant such as trans-resveratrol may help decrease BMI and improve reproductive potential in these patients [60, 61]. However, other authors have observed that resveratrol is unable to improve insulin sensitivity in rats with PCOS fed with normal chow [62]. Therefore, resveratrol may not be the most adequate candidate in this regard and should be taken cautiously.

An adequate exercise program is the first-line treatment with dietary changes to achieve weight reduction in obese patients with MetS or PCOS. Alterations in reproductive function due to physical activity and physical training have already been investigated, although with inconsistent conclusions due to a number of factors, such as training status, gender, and the different exercise protocols used [14, 15, 63, 64].

Nevertheless, intensive, strenuous training for competition seems to lead to altered hormonal profiles [65−67], testicular atrophy [68, 69], genitourinary problems [70, 71], altered semen parameters [72], altered oxidative status [14, 15], and menstrual abnormalities [73]. However, few negative effects have been described when performing regular moderate exercise ; and in this regard, active subjects show better hormone and semen profiles [63].

Increased adherence is achieved when physical exercise is integrated into a comprehensive program that includes group therapy and patient-specific nutrition. In the case of patients with PCOS, adherence to these changes not only achieves better range of objectives in weight and general well-being of the patient but also allows a better response to the drugs used to correct infertility.

The Clinical Guidelines on the Identification, Evaluation, and Treatment of Overweight and Obesity in Adults suggest performing physical exercise for 30–45 min, three to five times per week. All adults should set a long-term goal to accumulate at least 30 min or more of moderate-intensity physical activity on most, but preferably all, days of the week. We understand by moderate-intensity physical activity (60–70 % VO_2max; equivalent to 75–80 % HR_max) as any type of activity (cycling, running, swimming, or strength training) performed at least three times per week during a minimum duration of approximately 12 weeks [74].

Most of the studies published refer to training involving at least three 30-min aerobic sessions per week (e.g., 90 min/week) without dietary restriction or resistance exercise [75−77], although two studies reporting improvement included these components [78, 79].

Nevertheless, we would like to note that the activity adopted does not necessarily have to be of continuous low-intensity aerobic exercise. Using intense intervallic works (short-term, high-intensity interval training) may also provide beneficial effects on an elevated number of metabolic and vascular risk factors in overweight/obese, sedentary men [80, 81]. In these protocols, duration of each repetition must be short enough (≈ 5 s for supramaximal exercises and ≈ 30 s for submaximal exercises) and done at ample duration (≈ twice the effort duration) in order to get an elevated work volume during the session without getting to fatigue level.

Also, the inclusion of resistance training (RT) as an integral part of an exercise therapy program has been endorsed on Appropriate Intervention Strategies for Weight Loss and Prevention of Weight Regain in Adults by the American College of Sports Medicine [82], the Dietary Guidelines for Americans 2005 (USDHHS and USDA), and other of the American Heart Association [83] and the American Diabetes Association [84].

The American College of Sports Medicine [82] proposes to perform, at least, 150 min of moderate exercise per week to improve the health status in overweight and obese individuals. They also include a recommended goal of 200–300 min of leisure time activity per week for long-term weight maintenance. In the Dietary Guidelines for Americans, it is proposed to undertake at least 30 min of exercise on most days to improve health and 60 min of exercise on most days for weight loss and weight control.

In line with this, several studies show how exercise at least three times per week allows for reduction of fat percentage and risk factors associated with normal-weight and overweight sedentary subjects [85−87].

Endometriosis is a pathological condition commonly observed in women with infertility (6–10 % of women during their reproductive years; [88]). Endometriosis is characterized by the presence and growth of endometrial cells outside the uterine cavity, most commonly in the peritoneum [89]. These cells are influenced by hormonal changes and respond in a way that is similar to the cells found inside the uterus [90]. Endometriosis is characterized by a range of symptoms and severity, including chronic pelvic pain and infertility, with common presence of inflammation, scarring, and adhesions. As a result of these, many women may also suffer from infertility [91, 92]. Moreover, it has been suggested that endometriotic lesions release factors which are detrimental to gametes or embryos [93].

The role of modifiable exogenous factors such as nutrition and exercise in the development and/or prevention of this disease is not well understood. Nevertheless, recent evidence suggests there may be nutritional and exercise strategies to help ease the condition or even prevent it [94]. In an animal model study [95], it was found that fish oil could induce regression of surgically induced endometriosis . In humans [96], it was observed that the degree of endometriotic lesions was positively related to red meat consumption and inversely related to fruits and green vegetables consumption.

It has also been observed that N-acetyl-L-cysteine, besides having a beneficial effect on sports performance [97], also exerts a complex action on endometrial cells, involving regulation of gene expression and protein activity and location, with all of it converging into decreased proliferation and a switch towards a differentiating, less invasive, and less inflammatory phenotype [98].

It has been observed that markers of inflammation and interleukin-6 (IL-6) in women with endometriosis are modulated with fatty acid intake [99]. Although controversies exist [100], it has been observed that omega-3 fatty acids exert a protective effect on endometriosis risk; conversely, other foods such as red meat, trans fats, and coffee have affected this risk in a negative manner. Other authors have reported similar findings, encouraging increased omega-3 fatty acid and decreased trans fats intake in order to modify endometriosis risk [94].

Imbalance between ROS and antioxidant in the peritoneal fluid of some women has been shown to lead to oxidative stress and endometriosis [101−102]. In the presence of oxidative stress, ROS might increase the growth and adhesion of endometrial cells in the peritoneal cavity, leading to endometriosis and infertility [102].

Among the different nutrients in a diet , some seem to be especially interesting for the prevention and treatment of this pathology [103].

Despite the possibility of a certain degree of free radical being generated as a result of physical activity , and the effect this could exert on the development of inflammatory processes associated with endometrial tissue, there is evidence that regular physical activity has a protective effect on endometriosis, which possibly is favored by a hormetic mechanism [110].

The beneficial effects of exercise could be related to increase in cytokines and their anti-inflammatory potential [111]. The cytokine response to exercise is characterized by a constant increase in plasma IL-6 concentration [112, 113], in parallel with an enhanced expression of IL-6 mRNA in contracting muscles [114].

In addition, regular exercise is associated with changes in levels of circulating estrogens, with a reduction that could have a beneficial effect on the endometrium [115]. This effect can provide a protective effect since endometriosis is an estrogen-dependent disease and physical activity may increase levels of sex hormone-binding globulin (SHBG), which would reduce estrogen bioavailability [116, 117]. Physical activity also reduces insulin resistance and hyperinsulinemia [116], cell invasion, and proliferation and increases apoptosis on endometriosis lesions [117].

Endometriosis risk has been observed to be low in women who regularly exercise compared to those who do not [118, 119]. This observation, however, could be biased as women experiencing symptoms before being diagnosed may not engage in physical activity as much as healthy women do [119]. Total physical activity levels were weakly associated with confirmed endometriosis. Endometriosis risk was reduced by 11 % in the most active group when compared to the least active (≥ 42 metabolic equivalent (MET)-h/week vs. < 3 MET-h/week). Similar trend was observed in patients with no infertility but not in patients with infertility. When analyzing physical activity profile of the women 4 years prior to diagnosis, the observation was a 9 % reduction in risk for the more physically active women compared to less active women [119]. This observation is similar to the observation obtained from the most recent reported data [118] that women who reported frequent and regular high-intensity activity (> 30 min/session; > three times per week) for several years (2 years prior to the reference date) had a reduced endometrioma risk (76 %). Also, a nonsignificant reduction in risk was observed for women who reported such activity at ages 12–21 years. Moreover [120], it was observed that implementing a physical and psychological intervention protocol (one time per week; 2.5 h/session) in women with endometriosis was effective in reducing perceived stress, normalizing cortisol levels, increasing vitality, and improving physical functioning.