Why do I crave sweets when I can't taste them?

November 12, 2009 2:25 PM

I've lost my sense of smell/taste because of sinus congestion. Why do I still crave sweets after a meal?

For the past few days I haven't been able to smell much of anything and only taste very faintly, if at all due to the effects of a severe cold/flu. Why is it then that after I finish a meal, a meal that I can't even taste, I start looking around for the leftover Halloween candy? It doesn't seem like it's just out of habit but I really seem to crave something sweet after a meal even though when I eat the sweet, I can't taste that either. Somehow that satisfies the craving but how does my brain know I've eaten the sweet if I can't taste it? This has happened before when I've temporarily lost my sense of smell and I've never understood the underlying basis sensory processing. It's always seemed like such a waste to eat dessert to fulfill a craving but not even enjoy it! Could I blindfold myself and eat some tofu and trick my brain into thinking I had had a Reese's? Why doesn't that work?

posted by otherwordlyglow to science & nature (10 comments total)

You're craving the sugar/carbs that is in the Halloween candy so eating tofu would definitely not work to satisfy the craving. That's true with a lot of food cravings -- it's not about the taste (although that's certainly part of it) it's about what's in the food that your body wants.
posted by Kimberly at 2:27 PM on November 12, 2009

It's nothing to do with smell or taste; it's because you're eating carby dinners. Lower your carbs or eat a pickle, and the cravings will go after a week (as any low-carb dieter can tell you!)
posted by DarlingBri at 2:28 PM on November 12, 2009

Your intestine has sugar taste receptors. They don't really work to taste sugar in the way you think of, you don't register a sweet sensation, but instead detect the sugar and tell your brain and body that it's there. There are several other mechanisms by which your body measures food intake, not just amount but what types, and regulates appetite and metabolism appropriately. Some involve the brain, some only use the enteric nervous system, some focus entirely on signalling molecules and aren't neurophysiological. It's complicated and redundant. Being able to taste the food as it goes down is a very small part of this and most of it isn't affected by your cold.

You also have an elevated immune response going on which uses energy and changes your appetite. It's not surprising you're craving sweets, your body wants fuel to finish recovering from the infection. Again there are several overlapping complicated methods for controlling this.

If you're interested I can probably find a review article looking at at least some of this (let me know) but it's a pretty big and evolving field of research.
posted by shelleycat at 2:36 PM on November 12, 2009

I guess I'm not as interested in the sweets aspects of it specifically that just seems to be the most obvious example of what I'm after. (And how can you be sure I having "carby dinners"? That is not at all related to my question). My question really is, I guess, why do I care at all what I eat when I can't taste or smell it? Shouldn't I be happy eating stuff that I would normally consider bad-tasting but good for me?
posted by otherwordlyglow at 3:36 PM on November 12, 2009

Smell and taste are a important part of stimulating appetite. Our bodies are pretty well set up to keep you eating and not starving. You're more likely to eat things you like so your body is set up to want nice food.

But it's only a part of the issue. Your body, in general, wants to stay the same size. In particular satiety controls are very good at preventing starvation, although not so good at stopping overeating (hence the 'in general'). Kind of makes sense since getting enough food was a problem for more of our evolutionary history than having too much. Then add in things like infection, pregnancy, other dietary needs, and it's a sophisticated system. There are several different controls and feedback loops and mechanisms to measure what you eat, how big you are, your currently metabolic needs, and to keep you eating the right amounts of the right types of food. For this taste and smell aren't at all important, sensory stimulation isn't necessary.

So in this case your body wants sugar because that's what it thinks it needs, not because sugar tastes nice. There are a number of different things driving this, cytokines, neurophysiology, adipokines, taste receptors, etc. Of course our bodies are pretty well set up to think they need extra energy when maybe they don't, but given you're currently recuperating the sugar cravings are reasonable.
posted by shelleycat at 4:40 PM on November 12, 2009

how does my brain know I've eaten the sweet if I can't taste it?

Oh and this was the bit I was answering with taste receptors in your gut. There are receptors for other types of foods too, your body knows if you eat a bunch of protein for example (so no, tofu won't trick your brain). The sugar binds to it's receptor, the receptor then sends a signal to the brain telling it there was sugar. In this case there's no feedback giving you the sweet sensation like there would be on your tongue but it still registers inside. In fact the ones on your tongue are probably still registering too to some extent.

Seeing, tasting and smelling the food definitely adds to all this but it's only part of the picture. This is what I mean by redundant, there are several systems that acheive the same ends by different methods. This way someone who can't smell doesn't starve to death or eat the wrong things, the other systems contribute their effect or even take over entirely.

So in this case: "Shouldn't I be happy eating stuff that I would normally consider bad-tasting but good for me?" the answer is that actually you probably would be happy doing that. Except that in the sugar example your body has decided that sugar is good for you and you should be eating it regardless of what you think about it's taste or healthfulness.
posted by shelleycat at 4:50 PM on November 12, 2009

Your tongue's sense of sweetness isn't reduced by sinus congestion.
posted by IAmBroom at 5:27 PM on November 12, 2009

To add to that, I just got over a 2-week bout of Haemophilus, a.k.a. H-Flu, a bacterial infection with symptoms like the flu. Sense of smell & taste dropped off the map, desire to eat spicy food disappeared (GACK! What the...?!), but my cravings for sweets and salty foods shot up. Way up.

Part of that may have been my body craving quick calories, to keep the fever fires stoked (as far as craving sweets goes). Some of it, however, might have been a desire to have *some* taste in my food.
posted by IAmBroom at 5:29 PM on November 12, 2009

Your tongue has taste buds for salty, sour, bitter, sweet, and umami tastes. So while the sweets might not have much flavour — since this is determined mostly by the aroma you can't detect — they should still register as sweet on your tongue.
posted by parudox at 11:08 PM on November 12, 2009

What parudox said - same for the salty tastes IAmBroom mentions. You lose fine taste distinctions when your nose is out of commission, but salt and sweet still get there. This actually makes sense since salt and sugar are both very important to living (and bitter is important to not eating poison). So you may not be able to taste that it's a Snickers bar and not a Milky Way, but your brain still gets the 'sweet' message.
posted by Lady Li at 1:22 AM on November 13, 2009