Loss of Sex Drive and Libido from Dieting

Are you less interested in sex or dating than you were before you started dieting and losing weight? Or as one of the more animated participants of the Minnesota Starvation Experiment put it, do you “have no more sexual feeling than a sick oyster“? I know It sounds quite funny when it’s described so elegantly, but in all seriousness, a diminished sex drive can ruin relationships and negatively affect the well-being of chronic dieters, exercise addicts, and disordered eaters.

Minnesota Starvation Experiment

This article on sex drive and libido is part of a series that highlights the various symptoms that many experience from chronic dieting and overtraining. In order to examine these common symptoms, we will look at excerpts and quotes regarding the Minnesota Starvation Experiment, which is the most comprehensive study on caloric restriction and semi-starvation ever conducted. If you are not familiar with the study, or just need a refresher, you can read an overview of the study by expanding the two sections below.

Overview of Study

The Minnesota Starvation Experiment, which was conducted from 1944 to 1945 by Ancel Keys and his colleagues, included 36 healthy male participants, all of whom were men who were conscientious objectors of WW2. That is to say, they agreed to participate in the study rather than fight in the war. The purpose of the study was to examine semi-starvation with the goal of determining the most effective method of rehabilitating both starving citizens and prisoners of war come the end of the war. The observations and results of the study were meticulously recorded and later published in an over 1,300 page, two-volume book titled The Biology of Human Starvation.

Methods of Study

•Control Period (12 weeks): Approximately 3,200 calories per day, with the goal or creating a baseline for later comparison.

•Restriction Period (6 months): Approximately 1,560 calories per day and comprised of food similar to those found during times of famine: potatoes, rutabagas, turnips, bread and macaroni, etc. This period also included 22-miles of additional walking each week.

•Restricted Rehabilitation (12 weeks): The men were divided into four groups which consisted of either 400, 800, 1200 or 1600 more calories than during the restriction period. The highest calorie group was basically back to baseline calories, while the lowest calorie group was just under 2,000 calories.

•Unrestricted Rehabilitation (8 weeks): In the period, the men ate ad libitum, meaning that they ate as much as they wanted. For most men this ended up being around 5,000 calories per day, however, a few of the men ate as much as 11,500 calories on some days.

(Keys, 1950, pg. 70)

Does This Apply to Females As Well?

Before we get into the excerpts, I want to address a concern that some of the females reading this might be thinking: “Is a study on all men even relevant to me?”

This is a good question, and although there will obviously be some differences in the response of men and women due to factors such as hormones, there are actually more similarities than differences. In fact, you would probably be correct to expect that on average, a female’s libido and similar symptoms will be affected sooner and to a greater extent than in males. The evolutionary rationale for this gender difference is that a female’s body wants to make sure that there is adequate food before she begins to even think about having a baby.

Another major symptom that is common for women to experience is amenorrhea, which basically refers to the loss of the menstrual cycle. In addition to restrictive dieting, a common cause of amenorrhea is excess cardio. In fact, a study of female athletes reported that over 60% have at some point experienced Athletic Amenorrhea (Crouch, 2014). Just know that this is something women should look out for.

One more thing that I think I should mention: the following excerpts are from medical literature and therefore they can be explicit at times and sometimes “tell you more than you need to know” if you know what I mean. Just wanted to give that warning in case there are any young people who are reading this.

Libido & Sex Drive

Sexual feelings and expression declined in the Minnesota Experiment until by the end of the semi-starvation period they were virtually extinguished in all but a few subjects. The diminution of the strength of the sex drive was so dramatic that the subjects were struck by the change and used colorful language to describe it. As one of them put it, “I have no more sexual feeling than a sick oyster.” (Keys, 1950, p. 839-840).

General sex interest was reported by nearly all the subjects to have decreased. There seemed to be a definite decrease in the frequency of nocturnal emissions and erections (Keys, 1950, p. 840).

A marked reduction in the sex drive was observed throughout the period of reduced diet. Attraction to the opposite sex was much lessened. Sex dreams were not recalled, and nocturnal emissions and erections became less frequent (Keys, 1950, p. 820).

The Dutch observers noted general sexual depression. Libido was diminished or absent; flirtation was conspicuous by its absence; no sex jokes were heard. Among women menstrual disturbances, particularly amenorrhea, were widespread (Keys, 1950, p. 794).

Emotional response became progressively lowered and consciousness of sex was lost (Keys, 1950, p. 798).

The British prisoners of war were depressed and lost all sex interest. They “felt confused in their minds and were unable to concentrate on things like simple games and books” (Keys, 1950, p. 801).

Social withdrawal, narrowing of interests, obliteration of sexual drive, and difficulty in concentration were prominent (Keys, 1950, p. 906).

Less Interest in Relationships & Dating

The number of dates dropped drastically. Those who continued to date found their relationships strained. Some of the men were surprised to find that this was true even where their female contacts had appeared to be based on intellectual interests. Such situations probably stemmed from a decline in sociability as well as from the loss of sex impulses (Keys, 1950, p. 839-840).

His sexual interests dropped off severely in the early part of semi-starvation. At the beginning of the experiment he became acquainted with a girl with whom he had intellectually much in common. He was greatly surprised to note the degree to which semi-starvation reduced his interest in this friendship (Keys, 1950, p. 882).

Sex activities are reduced or cease. Sorokin distinguishes 3 mechanisms affecting this: a decrease in the physiologically determined sex drive, apathy toward indirect sex activities (such as courtship), and a supression of activities which are incompatible with food-seeking efforts (e.g. marriage and social gatherings) (Keys, 1950, p. 785).

This trend was reversed when the men returned to a normal, unlimited diet; normal sex interests reappeared, manifesting themselves in the desire to associate with women and in finding female companions attractive (Keys, 1950, p. 820).

How Long Does Sex Drive Take to Return?

This chart portrays the approximate severity and length that sex-drive was affected. The letters C, S, and R at the bottom represent the control, starvation, and rehabilitation periods respectively, while the numbers represent the number of weeks into the period. The libido curve is the one at the bottom. Sex drive took quote a long time to improve and was only about 50% recovered 12 weeks into rehabilitation (Keys, 1950, p. 823).

In the rehabilitation period, sexual impulses, needs, and interests were very slow in regaining their pre-experiment intensity; they were still low at the end of the twelfth week of rehabilitation (Keys, 1950, p. 839-840).

During rehabilitation, the recovery from dizziness, apathy, and lethargy was most rapid. Tiredness, loss of sex drive, and weakness were slow to improve (Keys, 1950, p. 828).

…dizziness and in apathy were most rapid and most complete, while tiredness, decrease of the sex drive, and weakness were slow to improve. Even at R12 (12 weeks into recovery), the men judged themselves to be far from the pre-starvation normal in these characteristics (Keys, 1950, p. 823).

13 weeks into recovery: No. 129’s sex interest was quite low; on the other hand, No. 104 had his first nocturnal emission on October 22 and No. 29’s sexual feelings were strengthened (Keys, 1950, p. 850).

15 weeks into recovery: social contacts with girls were as yet not appealing. No. 101 was becoming interested in women. The sex drive had returned to near normal in Nos. 123, 122, 1, and 127. In No. 11 sex interests had gone way up. for No. 29 food was no longer the focus of attention, and he did not feel anxiety when a meal was delayed; other interests, particularly those related to work and sex, overshadowed No. 127’s interest in food (Keys, 1950, p. 849-850).

33 weeks into recovery: 8 out of 12 men reporting considered their sex drive normal; 3 subjects rated their sex drive as strong or very strong; only in one case (No. 130) was sex interest still less intensive than before the experiment (Keys, 1950, p. 851).

Evolutionary Reason for This Change

The loss of the sex drive in semi-starvation is not an unmixed “evil.” Biologically it may be considered one of the adaptive mechanisms protecting the individual organism from nonessential energy expenditure (Keys, 1950, p. 839-840).

References:

Keys, A. B. (1950). The Biology of Human Starvation (Vol. I & II). Minneapolis: University of Minnesota Press.

Crouch, S. (2014, February 02). Is it Normal for Female Runners to Miss Their Period? Retrieved from https://runnersconnect.net/running-and-missed-periods/