No-one knows whether or not a neutral-tasting nutrient-sludge diet leads to enormous weight loss

February 15, 2023

I recently discovered the blog Slime Mold Time Mold, which is largely about the science of obesity — a matter of more than academic interest to me, and if I may say to, to Matt.

I discovered SMTM through its fascinating discussions of scurvy and citrus-fruit taxonomy. But what’s really been absorbing me recently is a series of twenty long, detailed posts under the banner “A Chemical Hunger“, in which the author contests that the principle cause of the modern obesity epidemic is chemically-induced changes to the “lipostat” that tells our bodies what level of mass to maintain.

I highly recommend that you read the first post in this series, “Mysteries“, and see what you think. If you want to read on after that, fine; but even if you stop there, you’ll still have read something fascinating, counter-intuitive, well referenced and (I think) pretty convincing.

Anyway. The post that fascinates me right now is one of the digressions: “Interlude B: The Nutrient Sludge Diet“. In this post, the author tells us about “a 1965 study in which volunteers received all their food from a ‘feeding machine’ that pumped a ‘liquid formula diet’ through a ‘dispensing syringe-type pump which delivers a predetermined volume of formula through the mouthpiece'”, but they were at liberty to choose how many hits of this neutral-tasting sludge they took.

This study had an absolutely sensational outcome: among the participants with healthy body-weight, the amount of nutrient sludge that they chose to feed themselves was almost exactly equal in caloric content to their diets before the experiment. But the grossly obese participants (weighing about 400 lb = 180 kg), chose to feed themselves a tiny proportion of their usual intake — about one tenth — and lost an astonishing amount of weight. All without feeling hunger.

Please do read the Slime Mold Time Mold write-up for the details. But I will let you in right now on the study’s very very significant flaw. The sample-size was two. That is, two obese participants, plus a control-group of two healthy-weight individuals. And clearly whatever conclusion we can draw from a study of that size is merely anecdotal, having no statistical power worth mentioning.

And now we come to the truly astonishing part of this. It seems no-one has tried to replicate this study with a decent-sized sample. The blog says:

If this works, why hasn’t someone replicated it by now? It would be pretty easy to run a RCT where you fed more than five obese people nutrient sludge ad libitum for a couple weeks, so this means either it doesn’t work as described, or it does work and for some reason no one has tried it. Given how huge the rewards for this finding would be, we’re going to go with the “it doesn’t work” explanation.

In a comment, I asked:

OK, I’ll bite. Why hasn’t anyone tried to replicate the astounding and potentially valuable findings of these studies? It beggars belief that it’s not been tried, and multiple times. Do you think it has been tried, but the results weren’t published because they were unimpressive? That would be an appalling waste.

The blog author replied:

Our guess is that it simple hasn’t been tried! Academia likes to pretend that research is one-and-done, and rarely checks things once they’re in the literature. We agree, someone should try to replicate!

I’m sort of at a loss for words here. How can it possibly be that, 58 years after a pilot study that potentially offers a silver bullet to the problem of obesity, no-one has bothered to check whether it works? I mean, the initial study is so old that Revolver hadn’t been released. Yet it seems to have just lain there, unloved, as the Beatles moved on through Sergeant Pepper, the White Album, Abbey Road et al., broke up, pursued their various solo projects, died (50% of the sample) and watched popular music devolve into whatever the heck it is now.

Why aren’t obesity researchers all over this?

8 Responses to “No-one knows whether or not a neutral-tasting nutrient-sludge diet leads to enormous weight loss”

  1. Note that the blog you’re talking about is written by a team of amateurs; that is not in and of itself a problem, but what is a problem is that they demonstrate some basic errors.

    I have an undergraduate degree in nutrition but no experience beyond that, but one of their claims was wrong on a very base level. That claim was, paraphrased, “Americans are only eating X calories more a day now than in the 1970s, that does not make enough difference to account for differences in obesity rate” – but putting those numbers into a simple BMR calculator show that it does. When this was pointed out to them, they made another post essentially moving the goalposts and stating “well, what we really want to know is WHY people are eating more”, while at the same time seeming to attempt to deny CICO.

    I suspect that the majority of their audience are intelligent people who want there to be a “lifehack” for body size manipulation.

    Here’s a blog post examining some of their claims in more detail:

  2. bjnicholls2 Says:

    Nutrient sludge? Given that all diets rebound or end up at an even higher setpoint when discontinued, I have a hard time imagining many people choosing a lifetime of drab, Kafkaesque feeding and social isolation rather than eating.

  3. Mike Taylor Says:

    The story with the nutrient sludge is not just it’s a diet you can stick to in order to lose weight, but that the tiny tiny sample of people who were on it found that they didn’t want to eat more. Also, the way the blog discusses this, the big question is whether this diet, unlike regular ones, resets the “lipostat” which the body consults to figure out how heavy to become.

    Of course there are loads of unknowns here. That’s my point. Those unknowns have been around for more than half a century, despite this one study being so potentially important, and no-one — apparently — has even tried to replicate or extend it.

  4. dale mcinnes Says:

    I know this reads a bit silly but the reasoning behind this just might be cultural. Not scientific. During part of that time, anorexia was considered the big problem. Funding might have gone there. Finding a way to lose weight was not sexy. Also the concept that everybody is different. Accept it. And “fat shaming” has taken on a negative quality. Always check out the culture of the times. It can and does affect the direction of funding in science.

  5. Mike Taylor Says:

    Well, Dale, I think that is a fine explanation for why no-one tried to replicate and extend this study in 1966, or indeed 1970. But it doesn’t come close to explaining why people aren’t falling over each other to do it in 2023.

  6. […] related to our work: No-one knows whether or not a neutral-tasting nutrient-sludge diet leads to enormous weight loss. You could try to replicate this with some […]

  7. fakename Says:

    Nutrient sludge is used for several different medical conditions (e.g. exclusive enteral nutrition therapy for inflammatory bowel disease, methionine free protein powder for some cases of homocysteinuria). One of the biggest problems with nutrient sludge is that it’s pretty gross and even when they mask it with different flavors, it gets pretty old pretty quick. Supposedly patients will sometimes buy several different types of formulas just so they can have a little variation in the taste. I imagine that while you may not feel hungry on such a diet, you would still crave real food!

    Some other things you may be interested in are the research on the keto-enteral nutrition diet and research on very low methionine diets (like mentioned above for cases of homocysteinuria). Very low methionine diets require you to eat such a low amount of methionine that you pretty much must eat a nutrient sludge. These diets have some very interesting results on rodent health and are being tested in humans.

  8. Mike Taylor Says:

    Thanks, fakename, all of that is really interesting.

    But, still, what fascinates me most is not so much the specific research question of this 58-year-old study, as the failure of any group, anywhere in the world (that we know of) to follow up on such a spectacular result with such obvious practical implications.

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