“I flew to Mars and Lost My Appetite”
When contemplating the excitement of aeronautical advancement, “menu fatigue,” well, isn’t on the menu. It’s not exciting. It’s not pretty. Although it might be preferable to The Phantom Menace, we’re not going to see a Star Wars prequel called Bored Taste Buds of the Old Republic.
That said, menu fatigue in space has already been an issue on previous missions, missions much shorter than our aspirations of Martian journeys and beyond. Whether we’re planning an exploratory mission of unprecedented interplanetary travel or a future ship full of garden variety space tourists, menu fatigue could prove to be the unexpected, boring wrench in our plans. Unless Star Trek-style replicators become a thing anytime soon, it’s a problem we need to figure out.
So, let’s start with the basics. What is menu fatigue, and why could it be a problem for long-term space travel?
What exactly is “Menu Fatigue?”
In general terms, “menu fatigue” (MF) refers to the boredom associated with repeated consumption of the same foods. It’s a problem restaurants have to consider when designing their menu and planning updates to continue attracting customers. As we’ll see, it causes a drop in the amount of food eaten, whether intentional or unintentional.
Most importantly, MF is a likely result of the psychophysiological phenomenon Sensory specific satiety (SSS). It’s not just a question of conscious boredom, but of an innate biological response.
SSS refers to “the decline in pleasantness associated with a food as it is eaten relative to ‘uneaten’ foods that have different sensory qualities.”1 When you’ve eaten a lot of a particular food, it’s SSS that makes you want to stop. However, if a different food becomes available, SSS subsides and you may resume eating. One study compared consumption when participants were offered a one-course meal vs. when they were offered a four-course meal. The participants ate a whopping 60% more when given multiple courses.1 This shows that the desire to eat isn’t just about hunger, but also perceived variety.
SSS: Habituation vs. Cognitive Response
Is MF/SSS a “low-level” response or a higher cognitive one? Prevailing assumption was the former, that SSS was driven mainly by habituation, which Oxford defines as “the diminishing of a physiological or emotional response to a frequently repeated stimulus.” A 2016 study conducted a series of tests to determine if SSS was mostly a physiological response or one of psychological/emotional boredom. Would perceived availability of a variety of foods affect the SSS of whatever food was being consumed?
In Round One, participants were given a sample of one lunch food and asked to rate pleasantness and desire to eat. Afterwards, they were given a full plate of the same food, advised that this was their lunch, and that they could have another serving if they wanted. When they’d had enough, they were again asked to rate pleasantness and desire to eat more. Not surprisingly, ratings for both declined significantly once participants were full and had consumed as much as they wanted of this particular lunch food.1
- Round One “No Uneaten Foods” TL;DR: 1) Rate a sample of this food; 2) Here’s a full portion – this is the only food you’ll get but you can have as much as you want; 3) Rate it again.
In Round Two, participants were offered bite-sized samples of four different foods and asked to rate them, again on pleasantness and desire to eat. They were then offered one of the foods and advised they could have as much as they wanted, but that the other three foods would not be available. After they had their fill of the one food, participants were asked to rate all four foods again.1
- Round Two “Unavailable Uneaten Foods” TL; DR: 1) Rate four samples of different foods; 2) Here’s an unlimited portion of one, but you can’t have the others; 3) Rate all four foods again.
Round Three followed the same protocol as Round 2, the difference being that participants were told they could switch to one of the other four foods after they consumed as much as they wanted of the first one and already completed the second round of ratings (they couldn’t have their “switch” food until they’d re-rated all four).1
- Round Three “Available Uneaten Foods” TL;DR: 1) Rate four samples of different foods; 2) Here’s an unlimited portion of one, and you will be able to eat as much as you want of another one after you rate again; 3) Rate all four again; 4) Now have as much as you like of your selected new food.
As expected according to SSS, Round One participants rated a significant decline in pleasantness and desire to eat more after they’d had their fill of the same food. No surprise there. But what if participants knew that another food would be available to them? Would that make their eaten food or uneaten food more desirable? Less desirable? Surprisingly, there was no significant difference in rating changes for any of the foods regardless of availability.1 Researchers conducted another round of studies in which they limited the portion of the eaten food rather than giving participants free reign. Results were the same.
What this study shows is that it’s not just a desire to eat another available food, or a longing for an unavailable food, that makes whatever someone is eating less appealing as they continue to eat it. Sensory specific satiety happens to a similar extent whether another food is available or not. Although SSS is generally considered a psychophysiology concept, evidence shows it leans heavily towards physiology. In other words, you can’t talk yourself out of becoming satiated with a particular food.
SSS in Amnesic Patients
Want some crazier evidence that SSS is physiological? A 2008 study (“Sensory Specific Satiety is Intact in Amnesics who Eat Multiple Meals”) probed the presence of SSS in several patients with amnesia. They intended to test the theory that impaired SSS is what often causes amnesic patients to consume multiple meals in succession, regardless of fullness.
Following cases of encephalitis, the patients in this study suffered from a form of amnesia related to lesions in the temporal and frontal lobes, impairing their ability to incorporate new memories.2 They were amnesic to the extent that they could not remember having just consumed a meal, often eating an entire new one if offered.
The patients and control group were tested with both multiple helpings of the same foods and with one meal of one type of food followed by a different type. Like in the aforementioned study, they were asked to rate their liking of the foods before and after. Predictably, the control subjects rated a decline in liking for foods that they had already eaten to satiety – but so did the patients with amnesia. There was no significant difference between the groups.2
One patient, after eating a cheese pastry to satiety, lowered his ranking when presented with it a second time. He described the taste of the pastry as an unpleasant “sour,” even though he had previously enjoyed it and had no memory of eating it in the first place. Like the control group, he opted for a previously uneaten food when offered a choice for his second helping. Researchers concluded that SSS appeared intact, even when memories of recently eating the satiated food were absent.2
Clearly, Sensory Specific Satiety has, at the very least, a strong physiological component. It’s not just about being picky or bored with repetitive choices. But if it’s about more than wanting to try something new and exciting, what would be the reason for it? After all, it seems that, from an evolutionary perspective, it would be more beneficial to be content with the limited choices around you. What might account for this innate response to eat less when confronted with lack of variety?
With its physiological stronghold, SSS can’t be without evolutionary reasons. An easy hypothesis is the need for nutrient diversity. If we’re content to eat one particular food for every meal with no satiation, we’re likely to miss out on whatever vitamins and minerals might be missing from that food. This would also explain why we experience a renewed interest in eating when presented with a new food choice (often dessert)3 even after we’re full (and why aforementioned study participants ate 60% more at a multi-course meal).
No false advertising from Jell-O, then. There really is “always room.”
“Jell-O provides relief from sensory habituation and re-invigorates your desire to eat more, regardless of satiation” might have been more accurate, but that one probably got a big thumbs down from the marketing team.
In an ancestral setting, the thought process was more like, Ugggghhh I’m so full of woolly mammoth I can’t eat another freaking bite or blubber will start pouring out of my ears oooooooh look, foraged cloudberries! Pass ‘em over! Boom. Now we have a dash of Vitamin C along with tasty woolly mammoth protein. No scurvy on this tundra.
There’s also the possibility that we evolved with SSS so that we would never eat too much of one thing, and therefore be spared the worst effects of tainted food. While this might be part of the explanation, it seems less likely since severe food poisoning can happen even with a little bite. And if something in nature is poisonous, it tends to be really poisonous. SSS won’t save you from a disagreeable mushroom.
When we look at our daily suggested amounts for vitamins and minerals, it’s not as simple as manufacturing the perfect pill that gives us all of them, every day, in the exact portion that we need. Most nutrition experts recommend vitamins to guard against deficiencies, but very few would encourage you to get all your essential nutrients this way. Prevailing advice is to get a good variety in your diet and take multivitamins to round things out.
Why can’t we just take a super-duper-all-inclusive-multivitamin and be done with it? Absorption conflicts. Some vitamins and minerals interfere with the absorption of others, making it difficult – if not impossible – to get everything you need from one single, repeated source.
A few absorption conflict examples:
- Zinc and copper – High intake of zinc can cause a copper deficiency. Zinc increases release of the intestinal protein metallothionein, which binds more readily to copper than zinc. Metallothionein binds to and traps copper in intestinal cells, preventing absorption and allowing more zinc to be absorbed instead.4
- Vitamin C and B12 – High doses of Vitamin C have been shown to destroy Vitamin B12 when taken close together, potentially causing B12 deficiency if C is repeatedly used in elevated amounts to colds and other bugs.5
- Vitamin E and Vitamin K – This one is more an issue of utilization interference than absorption. Vitamin E supplementation has been shown to increase bleeding in some individuals, while Vitamin K is known to assist in blood clotting. So, taking E with K can counteract K’s clotting effects.
- Calcium and everyone else – Okay, not everyone, but a few other minerals like phosphorus, zinc, magnesium, and iron.6 In They Might Be Giants terms, calcium is Triangle Man.
Additionally, even mere adequate intake of some vitamins and minerals can mask a deficiency of another, such as folate (B9) and B12. Absorption is complicated, and relying solely on a specially tailored multivitamin, though certainly better than nothing, might not be possible to meet all of our needs in the long term.
The absorption conflict explanation is especially relevant to our discussion of astrodietetics, since over-reliance on supplements could cause these issues. Could we figure out a series of supplements to take, in exactly the right amounts and at exactly the right times, so that they don’t interfere with each other? Possibly, but there’s a lot we still don’t fully understand about absorption and utilization, and at best it would be complicated.
So, here’s where we stand: Menu Fatigue, or Sensory Specific Satiety, is a physiological response that keeps us from wanting too much of any particular food. The habituation is so strong that it manifests in amnesic patients who don’t even remember eating the food that they’re suddenly tired of. Meaning it’s something we’ll have to deal with if we’re going to keep up proper nutrition on long-term space missions.
Coming up, we’ll take a look at:
- The proven effects of SSS on astronauts and the implications for long-term space travel
- Some possible solutions to combating menu fatigue
1. Wilkinson LL, Brunstrom JM. Sensory specific satiety: More than ‘just’ habituation? Appetite. 2016 Aug 1;103:221-228. doi: 10.1016/j.appet.2016.04.019. Epub 2016 Apr 20. PMID: 27105584; PMCID: PMC4910838. / 2. Higgs S, Williamson AC, Rotshtein P, Humphreys GW. Sensory-specific satiety is intact in amnesics who eat multiple meals. Psychol Sci. 2008 Jul;19(7):623-8. doi: 10.1111/j.1467-9280.2008.02132.x. PMID: 18727773. / 3. Heshmet S. “Why do you always have room for dessert?” Psychology Today, 15 Sept. 2016, https://www.psychologytoday.com/us/blog/science-choice/201609/ why-do-you- always-have-room-dessert. / 4. Higdon J. “Copper.” Oregon State University, Linus Pauling Institute. https://lpi.oregonstate.edu/mic/minerals/copper. / 5. Herbert V, Jacob E. Destruction of Vitamin B12 by Ascorbic Acid. JAMA. 1974;230(2):241–242. doi:10.1001/jama.1974.03240020031018 / 6. “Calcium.” Harvard School of Public Health. https://www.hsph.harvard.edu/nutritionsource/calcium.