This post has been translated into Russian by Polina here.
I have often heard anorexia nervosa sufferers complain of “memory gaps,” particularly during the times they were really sick. As if they weren’t really there. It can be scary and unnerving, to say the least. A few months ago, a Tumblr user asked me about this:
Hi Tetyana, I’m not sure if this is merely based on my own subjective experience of if there is any grounding at all, but I was wondering if there could perhaps be a link between EDs and a sort of memory loss. It’s hard to describe but I definitely seem to have huge “gaps” in my memory of during that time, as if I selectively block things out. I have limited inaccurate knowledge with regards to memory on a molecular/neurological basis so I do not know if there’s anything there. Perhaps with calorie restriction in anorexia nervosa there is simply not enough “energy” for memory to function adequately? I don’t know whether there is a link here and how far a sort of “memory loss” is experienced by those with anorexia and other EDS and if so, why.
I researched the question a bit myself and what was meant to be a short responses turned into a 1,000+ word answer.
In this post I’ll expand on my answer, and so it will be different from what I usually write. It won’t be an in-depth analysis of one or two studies. Instead, I’ll guide you through my thought process in answering this question and what I found during my search.
Importantly, I am not expert on this topic and I have not done a thorough search, which is to say: this is not comprehensive and your ideas/thoughts are always welcome.
When I first read the question, I thought, assuming this is something that is true and replicable among many with eating disorders (or just anorexia nervosa), the phenomena might be due to deficits with learning OR memory OR recall (among other things). Each of these are separate things and can be teased apart experimentally (Well, at least in rats and mice, I don’t know much about human research on learning and memory.)
A lot of things immediately sprung to my mind about what could be happening. Maybe it is lack of energy (glucose) during the acute AN phase for actual cellular function, or maybe it is due to impairment in hippocampal neurogenesis (the hippocampus is crucial for learning and memory), or maybe it is a trait (something that existed before the onset of the ED), or maybe it is due to a preoccupation with food/weight which leaves little “mental space” for other learning and memory to occur? A lot of possibilities, and those are just some that came to mind.
I figured that a good way to “test” the idea that learning and/or memory impairments might be due to lack of energy (calorie restriction) would be research the findings in the calorie restriction (CR) field. CR has been linked to longevity and there are accumulating studies in primates on the effects of CR not only on longevity but also on cognitive function.
I found one study in humans that suggested that a CR diet actually IMPROVED memory. (Although the mean age of the sample was 60.)
This interventional trial demonstrates beneficial effects of caloric restriction on memory performance in healthy elderly subjects. Mechanisms underlying this improvement might include higher synaptic plasticity and stimulation of neurofacilitatory pathways in the brain because of improved insulin sensitivity and reduced inflammatory activity. Our study may help to generate novel prevention strategies to maintain cognitive functions into old age.
Then I found another (small) study, a 6-month randomized controlled trial, that showed CR did not have any negative effects on learning, memory or cognition.
This randomized controlled trial suggests that calorie restriction/dieting was not associated with a consistent pattern of cognitive impairment. These conclusions must be interpreted in the context of study limitations, namely small sample size and limited statistical power. Previous reports of cognitive impairment might reflect sampling biases or information processing biases.
So, if this is true, it suggests that calorie restriction and energy deficit alone do not play a huge rule of learning/memory deficits in AN. Of course, this is under the assumption that the “memory gaps” experienced by the OP, and by others I have talked to is linked to anorexia nervosa. That may not be the case.
Next I thought: what are the effects of dieting as opposed to calorie restriction on cognitive function? There have been a bunch of studies (mostly by the same group, though) that have shown that self-initiated dieting has negative impacts on cognitive function (such as learning and memory):
Vreugdenburg, Bryan & Kemps (2003) found that, compared to non-dieting controls, individuals who were dieting performed worse on cognitive tasks. They found that the higher levels of preoccupying cognitions in the dieters, the worse the functioning of the “central executive.” That’s stuff like learning, memory, attention, reasoning, and task switching.
Kemps, Tiggemann, & Marshall (2005) also found that dieters, compared to controls, performed poorly on various tasks testing working memory and other cognitive functions. They suggested that the preoccupying thoughts about food, weight, and body shape were responsible for the decrease in cognitive functions. They hypothesized that preoccupation with these issues (dieting, food, weight, shape) take up a lot of “mental space” and leave little for other tasks. The same group reported a similar finding in another study, too.
These cognitive deficits are due to psychological mechanisms underlying the process of being on a diet rather than to physiological consequences of weight loss. For example, experimentally manipulated food deprivation for 24 h (Green, Elliman, & Rogers, 1995) or even several months (Kretsch, Green, Fong, Elliman, & Johhson, 1997) does not impair cognition. More specifically, the act of dieting has been linked to an increased preoccupation with thoughts about food, eating, weight and body shape (Jones & Rogers, 2003; Rogers & Green, 1993). Such preoccupying cognitions are thought to reduce the amount of working memory capacity available for cognitive task performance (Green, Elliman, & Rogers, 1997).
It is important to keep in mind that the above studies compared dieters with non-dieters, NOT individuals with anorexia nervosa to non-dieters or dieters.
So what about studies on learning and memory in anorexia nervosa patients?
There was a study published in 2010 by Nikendei and colleagues that found impaired memory performance in patients ill with AN but they also found that these deficits persisted after weight-restoration. They concluded that “the findings suggest that impaired memory performance is either a stable trait characteristic or a scar effect of chronic starvation that may play a role in the development and/or persistence of the disorder.”
Personally, I don’t buy the stable trait idea. I’m not even sure I buy the scar effect–though I would suppose that would depend on the illness severity/duration versus length of remission, maybe.
In their introduction, Nikendei et al reviewed the contradictory findings with regards to learning and memory in AN:
However, studies that have focused on various facets of general memory performance have shown a range of contradictory results. Some authors have reported immediate (Hamsher et al. 1981; Jones et al. 1991; Green et al. 1996; Kingston et al. 1996; Mathias & Kent, 1998; Bayless et al. 2002; Moser et al. 2003) and delayed (Jones et al. 1991; Mathias & Kent, 1998; Bayless et al. 2002) verbal recall deficits in acute AN patients whereas others have revealed normal (Szmukler et al. 1992; Mathias & Kent, 1998; Lauer et al. 1999; Moser et al. 2003; Connan et al. 2006; Nandrino et al. 2006; Bosanac et al. 2007) or even superior (Hatch et al. 2010) immediate verbal recall and normal delayed verbal recall (Kingston et al. 1996; Mathias & Kent, 1998; Nandrino et al. 2006; Bosanac et al. 2007; Hatch et al. 2010).
Nikenei et al. pointed out that imaging studies (Wagner et al., 2007) do not suggest there are any structural changes in the hippocampus (which, as I mentioned above, is important for learning and memory, and it is also one of two brain regions in adults where neurogenesis (the birth of new neurons) occurs). But of course, deficits can easily occur on a level that’s undetectable by conventional brain imaging techniques.
So, there’s no definitive answer (as far as I can tell right now), but it might be that AN (or eating disorder) related obsessions “take up mental space” and interfere with cognitive functions. This also makes sense give the findings which have suggested that patients with AN have a “memory bias” toward ED-related things (food, weight, calories), which I’m sure is something that all readers who have experienced an eating disorder can attest to. (For more on that, see: Sebastian et al. 1996; Hermans et al. 1998; Williamson et al. 1999; Pietrowsky et al. 2002; Lee & Shafran, 2004; Suslow et al. 2004; Nikendei et al. 2008; Tekcan et al. 2008.)
Readers, what do you think? Have you experienced these “memory gaps”? What else, that I’ve overlooked, might be helpful in answering this question? Or is there an answer (perhaps a study) that I missed in my search?
Kemps E, Tiggemann M, & Marshall K (2005). Relationship between dieting to lose weight and the functioning of the central executive. Appetite, 45 (3), 287-94 PMID: 16126305
Martin, C., Anton, S., Han, H., York-Crowe, E., Redman, L., Ravussin, E., & Williamson, D. (2007). Examination of Cognitive Function During Six Months of Calorie Restriction: Results of a Randomized Controlled Trial Rejuvenation Research, 10 (2), 179-190 DOI: 10.1089/rej.2006.0502
Nikendei C, Funiok C, Pfüller U, Zastrow A, Aschenbrenner S, Weisbrod M, Herzog W, & Friederich HC (2011). Memory performance in acute and weight-restored anorexia nervosa patients. Psychological medicine, 41 (4), 829-38 PMID: 20529417
Vreugdenburg L, Bryan J, & Kemps E (2003). The effect of self-initiated weight-loss dieting on working memory: the role of preoccupying cognitions. Appetite, 41 (3), 291-300 PMID: 14637328
Witte AV, Fobker M, Gellner R, Knecht S, & Flöel A (2009). Caloric restriction improves memory in elderly humans. Proceedings of the National Academy of Sciences of the United States of America, 106 (4), 1255-60 PMID: 19171901