Why are female rats more likely to binge eat than male rats?

Binge eating is a phenomenon where someone may start eating but then find it difficult to stop. I actually think that binge eating is more common than perhaps is recognised. Lots of lots of people will, for instance, find that what started as ‘just one biscuit’ turns into half a packet or that a few crisps/chips turns into the demolishing of a big bag or tube. A similar thing can happen with a wide variety of foodstuffs including chocolate and alcohol.

There is a perception, I think, that binge eating is more common in women. My experience is that this is generally true. I also believe that sometimes an unconscious assumption is made that this relates to the fact that women are more likely to be weight-conscious and ‘on a diet’. The problem with being on some restrictive eating regime is that it can induce hunger which can stimulate binge-eating. Sometimes, the bingeing will lead to purging, and repeated cycles of these behaviours are usually classified as ‘bulimia nervosa’ or ‘bulimia’ for short.

Again, here, there is sometimes the idea that the problem stems from a desire for weight control and maybe increased societal pressure on women to conform to a certain size and shape. These factors may play a role, but if I’ve learned one thing about eating behaviour in my time as a doctor it’s that bingeing can often be related to biochemical imbalance.

For example, the mid-late afternoon is a time when blood sugar levels can tend to drop a bit, and this does seem to have the capacity to cause an individual to crave food, particularly those that replenish sugar quickly into the system such as chocolate/candy or biscuits/cookies. Sometimes I see people who believe their drive to eat sweet foods is rooted in a weak will or lack of self control. The reality is, though, that once these individuals eat in a way that is stabilising for blood sugar levels, their desire for these foods usually melts away and becomes a non-issue.

A piece of research just published also suggests that binge-eating may have a physiological basis. This research, in essence, found that female rats were twice to six-times more likely to binge eat compared to male rats [1]. I suppose it’s possible that female rats feel under increased pressure to conform to some rodent ideal in terms of shape and size, but I suspect not. More likely, is that the increased tendency to binge eat is driven by something different in the rats’ biology.

rat image

One potential candidate here concerns the brain chemical serotonin. This ‘neurotransmitter’ generally induces feeling of happiness and calm in the brain. However, should levels of it fall, the body may be driven to take steps to drive serotonin levels up in the brain. This is believed to be a potential factor in some peoples’ eating behaviour, and in particular a tendency to binge on carbohydrate foods.

The proposed mechanism here concerns the amino acid (building block of protein) tryptophan. In the brain, tryptophan can be converted into 5-hydroxytryptophan (5-HTP) which can be then converted into serotonin. The trick would be to get more tryptophan into the brain. Eating carbohydrate induces the secretion of insulin which sweeps amino acids out the bloodstream. However, insulin leaves tryptophan relatively untouched, which means it gets ready access to the brain (it doesn’t have to compete so much with other amino acids for brain entry). Here, higher levels of tryptophan can lead to a boost in serotonin which can then have the desired effect (improved mood).

So, it’s conceivable, then, that in some people, binge-eating is driven by serotonin depletion. In one study, women with a history of bulimia (but recovered) were fed a tryptophan depleted mix [2]. Compared to when they were fed a mix with tryptophan in it, this led the women to subjective feel less in control of their eating. The tryptophan-depleted mix also lead to lowered mood and increased concerns over body image.

It is possible for serotonin levels to deplete over the course of the day, and this may help explain why some people are prone to overeating and bingeing in the evening or even in the middle of the night.

One simple way to boost serotonin levels is to seek sunlight exposure. The amount of sunlight exposure we get appears to be quite strongly tied to the amount of serotonin we make in the brain [3].

Supplementation with either tryptophan or 5-HTP is another valid strategy. The sort of dosages that are usually useful here are 500 – 1000 mg of tryptophan or 50 – 100 mg of 5-HTP taken between meals (which is believed to help absorption).

If first got to know about the use of these (and other) amino acids in the treatment of binge-eating and mood issues by reading the work of nutritionist Julia Ross (author of The Mood Cure and The Diet Cure). These books, I think, are well worth a read by people interested in how they may use targeted amino acid supplementation to naturally control their eating and improve their mood.


1. Klump KL, et al. Sex differences in binge eating patterns in male and female adult rats. International Journal of Eating Disorders, 2013; DOI: 10.1002/eat.22139

2. Smith KA, et al. Symptomatic relapse in bulimia nervosa following acute tryptophan depletion. Arch Gen Psychiatry. 1999;56(2):171-6.

3. Lambert GW, et al. Effect of sunlight and season on serotonin turnover in the brain. Lancet. 2002;360(9348):1840-2.

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9 Responses to Why are female rats more likely to binge eat than male rats?

  1. Christoph Dollis 2 May 2013 at 10:03 am #

    The need to maintain a higher body-fat level for pregnancy and nursing?

  2. EE 2 May 2013 at 3:34 pm #

    “So, it’s conceivable, then, that in some people, binge-eating is driven by serotonin depletion. In one study, women with a history of bulimia (but recovered) were fed a tryptophan depleted mix [2].”

    So the mix actually reduced the amount of tryptophan already within the bodies of the subjects? Or just the availability of tryptophan?

    This is a topic I am greatly interested in. As a formerly-recovered bulimic who has recently suffered a bad relapse I can tell you that the drive to overeat always comes when my mood is low. I was not bulimic prior to starting a low carb diet over three years ago, but significant weight loss via the diet alone and no E.D. (to a barely “underweight” state) seemed to trigger a massive urge to binge. I regained all the lost weight and developed bulimia.

    And now I feel “stuck” with low carb eating (mostly lc veggies and meat, some dairy)–if I reintroduce carbohydrates in any form it immediately triggers out of control eating, not to mention jacks my blood sugar from a steady 75-80 to 150+. And yet, I still often feel apathetic and have low energy trying to eat LC–these are the times I crave carbohydrates. So I end up eating carbs, then overeating (because I have not been able to stop the process once it begins…but I always try), then feel awful and either purge or over-exercise to compensate.

    It’s all very f*cked and I feel bad for other recovering bulimics trying to get a grip. Not easy to overcome when it’s the only way your brain gets a “hit” of contentedness and calm.

  3. david manovitch 3 May 2013 at 9:31 am #

    I am very suspicious of single cause theories and especially where a single chemical is involved. This usually allows the drug pushers to leap gleefully on the gravy train with a magic bullet or is it bollocks cure. Fortunately SSRIs have already been invented. They are not hugely effective though in treating bulimia nervosa

    Furthermore extrapolation from animals to humans is illogical and dangerous. Bulimia Nervosa is a complex condition with no doubt biological, psychological and social elements and cannot and should not be reduced to the mythical chemical imbalance so beloved by the medical profession and the pharmaceutical companies.

  4. moo 3 May 2013 at 9:44 am #

    wow I feel for you I’ve found lowcarb lifestyle the only sustainable weight maintenance methodHowever fine tuning and wake upcalls are part of it Check your intake carefully perhaps on carb creep , food scale and carb counting application can be helpful Even a “pro”can lose track. of exactly how many total carbs one is taking inMedications can affect weight such as beta bloccurs,anti psychotics etcEven a pro can be in denial about certain health or dietary intakes and rationalise into altering the balance Do not give up the efforts that worked before sometimes we learn the lesson after several tries and find some tricky mis step that screws us up
    If diabetes is developing but not yet diagnosed, ones blood sugar levels could be even more unstable and require tighter carb restriction Also not toomuch caloric restriction in terms of adequate protein and fats to give one energy A check up for other possible fatigue causers could be considered Any toxic habits such as tobacco or alcohol use?
    you may want to rule out other issues sleep disorders?depression?cardiac,thyroid,hormonal etc etc

  5. Dr John Briffa 3 May 2013 at 10:32 am #


    To be clear, i’m not saying that serotonin depletion is the cause of bulimia, just a potential cause.

    And rather than throw our hands up and say ‘it’s complex’, how about trying things that have some rationale to them and might actually help or work?

  6. eddie watts 3 May 2013 at 5:41 pm #

    i’ve seen elsewhere that boosting protein has been shows to improve female’s mood when they have mood problems too.
    and as carbohydrate binging tends to displace protein intake, as opposed to fat say, this could help with both issues.

  7. Pauline 7 May 2013 at 12:09 pm #

    I also think this is a complicated picture and we only have some of the pieces.

    My personal experience is that being iron deficient triggers the most terrible food cravings… and I would grab whatever came to hand. In most cases, easily accessible food is also of the junk variety, and chocolate usually fits the bill. 🙂

    I understand that iron is needed to manufacture both serotonin and dopamine – both brain chemicals that affect our mood. So that kind of fits with the food cravings/serotonin theory.

    (Why does serotonin get all the headlines? Whatever happened to poor old dopamine?)

    It was definitely not the sugar that I was craving as I get more satisfaction from “real food”, but it is hard to lay your hands on a gourmet dinner at short notice in the middle of the afternoon!

    I suspect that a lot of people with serious food cravings are nutrient depleted… but they don’t understand what their body is trying to tell them.

  8. Tracey Greenwood 3 June 2013 at 10:14 pm #

    I find it astonishing that tryptophan/5-HTP isn’t available on prescription in the UK (I believe it’s licenced for prescribing in the US). I researched a more ‘natural’ treatment for my husband’s anxiety, rather than see him suffer longer on standard SSRIs/anti depressants. On 5-HTP, his mental health improved dramatically over literally a couple of weeks, but after a visit to the GP – who told us it’s not available for her to prescribe – he had to settle for paying up to £30 a month for his supply of 5-HTP. Yet 5-HTP has virtually ZERO side effects, compared to the manufactured and licenced SSRIs, which also can take weeks – if not months – for the patient to start seeing any kind of improvement in their condition.

  9. Sandra C 15 November 2013 at 12:00 pm #

    Okay so this has no basis in science and is an unsubtle observation. My family and I divide our outlook on life as being either ‘rat’ or ‘pig’ (we have affection for both animals as both have been much-loved pets I should add). Those exhibiting rat-like behaviour are wonderfully self-controlled, like my husband, who has no problem when given a box of chocolates, in making it last for 3 months, occasionally going to his cupboard (he has Coeliac Disease so it’s easier if all his food is on one cupboard) and having a single chocolate. We observed similar hoarding behaviour in our pet rats (sometimes discovering half a sausage hidden somewhere in my daughter’s room). They knew when they’d had enough and were happy to heep their stash for another day. Then there are those of us who are pig-like. It’s a struggle not to keep eating the tube of Pringles so the only thing to do is not buy it. We exercised great control in not raiding my husband’s cuboard, knowing that he had wonderful stuff in there and it was tormenting us!. Like our pet pigs, it’s as if we have some hidden message that says ‘if you don’t eat it now some other bugger will come and eat it’. These attitudes seem to pervade other apects of our lives – no impulse buying for my husband – he doesn’t even think about it – for us ‘pigs’ we have to give ourselves a good talking to in order to avoid it. As I said, there is no science in this just an observation that as a family we were more akin to some pets and their approach to life than others.

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