Nevertheless, the phases of sexual behavior remain very similar to eating behavior. For example, the refractory period after ejaculation is very similar to the satiety after a meal, likewise the rhythmicity of vaginal thrusting and chewing food [2].
On the whole, alimentation and sexuality are composed of a motivational part, hunger and libido, and a consummatory part, i.e., the eating and the coitus.
Additionally, both the sex and the food phases are modulated by internal state, such as the blood levels of sex steroids or nutrients, prior experiences, or associations. The cerebral area involved in the reward and reinforcement processes concerning the motivation to partake in food and sex is the orbitofrontal cortex, which elaborates the associations of sex and food representations with a positive or negative judgment [2].
The other neuroanatomic areas involved in the phases of anticipation, consummation, and satiety in both sexuality and alimentation are the insula, the anterior cingulate cortex, and the amygdala ventral striatum. Moreover, it is known that the olfactory system is also central to the choice and consumption of food, and sexual behavior is also influenced by odors and perfumes. In particular, pheromones play a central role in the mating strategies of animals, and also of humans through the vomeronasal organ, which sends signals to the hypothalamic areas [2]. On the other hand, the quality of the stimuli is fundamental for choice and motivation, both in terms of sexuality and eating behavior.
14.2 Prevalence Data of Sexual Dysfunction in Obese Men and Women
In addition to medical, physical, psychosocial, and emotional consequences [10, 11], obesity is linked to both sexual dissatisfaction and/or sexual difficulties [12]. From 1966 and onwards, research studies have examined the relationship between obesity and sexual quality of life.
A US study on sexual dysfunction in obese population has reported prevalence rates of 7–22 % for women (sexual pain, arousal problems, and low desire) and 5–21 % for men [erectile dysfunction (ED) hypoactive sexual desire disorder and premature ejaculation] [13].
One of the most common sexual dysfunctions in obese men is represented by ED. Many studies have found a positive association between high levels of BMI and ED [14–16].
For example, in a cross-country study on the prevalence of ED in several countries (including the USA and five European countries), a clear relationship emerged between weight and male sexual function [15]. In fact, the prevalence in normal-weight men was inversely related to ED, whereas among overweight men there was no relation to ED while obesity is directly related, indicating that there is a correlation only among obese men.
A higher prevalence of ED in obese men has also been indicated in data from other surveys. For instance, it was reported by some follow-up studies [17, 18] that body weight was an independent risk factor for ED, with a risk exceeding 90 % of controls (odds ratio between 1.93 and 1.96, respectively).
Another study [18] shows that among younger Danish men, the odds of having ED and/or retarded ejaculation were greater for those with high BMI than for those with low BMI. Results were significant for ED in relation to BMI >30 kg/m2, whereas premature ejaculation and sexual desire were unrelated to BMI. The association between ED and a BMI >30 kg/m2 remained significant for younger, but not older men (See Table 14.1).
Odds ratios (95 % confidence intervals) | |||
|---|---|---|---|
BMI (kg/m2) | <25 | 25–29.9 | >30 |
Erectile dysfunction | |||
20–45 years | 1 (reference) | 1.22 (0.5–2.5) | 2.74 (1.1–6.8) |
50–75 years | 1 (reference) | 1.00 (0.6–1.8) | 1.40 (0.6–3.1) |
Premature ejaculation | |||
20–45 years | 1 (reference) | 0.86 (0.6–1.2) | 1.19 (0.7–2.0) |
50–75 years | 1 (reference) | 1.23 (0.7–2.1) | 1.58 (0.7–3.4) |
No sexual desire | |||
20–45 years | 1 (reference) | 1.05 (0.4–2.4) | 0.39 (0.1–3.1) |
50–75 years | 1 (reference) | 1.43 (0.6–3.6) | 1.08 (0.3–4.5) |
Retarded ejaculation | |||
20–45 years | 1 (reference) | 0.33 (0.1–1.2) | 1.30 (0.3–4.8) |
50–75 years | 1 (reference) | 0.97 (0.4–2.2) | 0.90 (0.3–3.1) |
Although overweight and obesity are clearly implicated in sexual dysfunction in men, the relationship between female sexual function and obesity is not well known yet. Evidence linking female sexual disorders (FSD) to obesity is insufficient. In a study with postmenopausal women [19], it was reported that the degree of reduced sexual interest is significantly related to body weight.
On the other hand, Esposito et al. [20] discovered a negative relationship between body weight and sexual function in 52 women with abnormal values of FSFI (score <23), showing that obesity affects several areas of sexual function unlike healthy women with FSD: arousal, lubrication, satisfaction, and orgasm, but not desire and pain (Fig. 14.2).
Fig. 14.2
Individual domains of female sexual function in women with metabolic syndrome (SM) and in control women (From Esposito et al. [20], modified)
Data from a study based on a sample of obese women preparing for bariatric surgery [21] confirm the results of Esposito’s study, except for the area of desire, which is significantly lower in the sample of obese women than in the control group.
Finally, a study concerning gender differences regarding sexual quality of life in obesity [22] compared Sexual Life item responses by BMI category (Class I, II, and III obesity) and sex (Table 14.2). In line with previous studies, significant differences are reported by the BMI group for all Sexual Life items, except for sexual desire. Subjects with BMI >40 kg/m2, compared with the other two groups of obese subjects, had less sexual enjoyment, more difficulty with sexual performance, and greater avoidance of sexual encounters.
BMI category | |||||
|---|---|---|---|---|---|
Class I | Class II | Class III | |||
(30–34.9 kg/m2) | (35–39.9 kg/m2) | (>40 kg/m2) | |||
(n = 159) | (n = 277) | (n = 722) | p | Post hoc | |
Do not enjoy sexual activity | |||||
Women | 2.34 ± 1.36 | 2.59 ± 1.33 | 3.00 ± 1.46 | <0.001 | III>II>I |
Men | 1.68 ± 1.02 | 1.93 ± 1.14 | 2.11 ± 1.36 | <0.001 | F > M |
Have little sexual desire | |||||
Women | 2.89 ± 1.32 | 2.72 ± 1.31 | 3.09 ± 1.41 | 0.109 | |
Men | 2.29 ± 1.22 | 2.41 ± 1.23 | 2.43 ± 1.27 | <0.001 | F > M |
Difficulty with sexual performance | |||||
Women | 2.31 ± 1.37 | 2.55 ± 1.36 | 3.08 ± 1.41 | <0.001 | III>II>I |
Men | 2.17 ± 1.05 | 2.58 ± 1.25 | 2.78 ± 1.40 | 0.173 | |
Avoid sexual encounters | |||||
Women | 2.67 ± 1.46 | 2.72 ± 1.43 | 3.02 ± 1.52 | 0.002 | III>II,I |
Men | 1.88 ± 0.98 | 2.15 ± 1.12 | 2.35 ± 1.38 | <0.00 | F > M |
Women reported greater impairments than men in sexual enjoyment, desire, and avoidance of sexual encounters, but did not differ in terms of difficulties with sexual performance.
14.3 Sexual Distress in Obese Men and Women
Obesity is a medical condition implying a series of numerous comorbidities, such as type 2 diabetes [23], hypertension [24], cardiovascular disease [25], osteoarthritis [26], certain malignancies, and premature mortality [27]. In addition, obesity is often associated with an impairment in general health-related quality of life (HRQoL) [28–30]. An important aspect of quality of life is sexual well-being. However, this aspect is often underestimated as a potential cause of distress in people affected by extreme obesity. The relationship of obesity with sexual functioning is a multifactorial phenomenon; in fact, sexuality in obese people may be jeopardized not only by weight-related comorbidities but also by reproductive hormones and many psychosocial factors.
14.3.1 Sexual Distress Due to Weight-Related Comorbidities
Literature evidence clearly shows the impact of weight-related comorbidities on sexual functioning [30, 31]. Due to a high BMI, obese people have a great probability of developing in their life type 2 diabetes, which is often preceded by insulin resistance and hyperinsulinemia. These conditions determine changes in sex hormones [31], these being a decrease in testosterone levels in men and increased levels of free testosterone, C19 steroids, and estrogen levels in women [31]. These hormone changes cause ED in men and decreased desire and decreased vaginal lubrication in women, conditions that may also have a bearing on the frequency of sexual intercourse.
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