In which an absolutely stupid experiment is described, which doesn't show what the experimenters think that it shows. Frankly, I'm not even sure if it shows anything at all, apart from the fact that nutrition research might be a great career for you if you have a double-digit IQ. We're then treated to "a professor of nutrition at Tufts University" who witters on about the dire state of nutrition science.
I'm pretty sure you don't need to have a science background to spot the problems with the experimental procedure and interpretation of the result, so hopefully it has some amusement value for all of the members here.
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TheAwfulToad
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I'm not sure where to even start, but if you follow the link to the whole paper, my comments are referring to that.
The first point to note is that there is no hypothesis. It's hard to even infer one. They appear to have lots of questions and can't seem to decide which one they want to address with their experiment. So they just do some stuff and hope something useful drops out ... ie., "fishing for results".
"Dietary carbohydrate restriction has been purported to cause endocrine adaptations that promote body fat loss more than dietary fat restriction."
That's inaccurate, and an almost universal misunderstanding among LCHF opponents. LCHF does not "promote body fat loss". It corrects the metabolic malfunctions that ultimately lead to obesity, thereby reversing it. While that might seem to be splitting hairs, my point is twofold:
a) A normally-functioning human body simply does not become obese. "Body fat loss" is not something that even needs to happen except in a chronic subclinical disease state.
b) "Body fat loss" is not an end in itself. You can achieve body fat loss very effectively by not eating for three weeks. The aim is to stay slim, ie., to correct the underlying metabolic dysfunction.
"...with proponents claiming that the resulting decreased insulin secretion causes elevated release of free fatty acids from adipose tissue, increased fat oxidation and energy expenditure, and greater body fat loss than restriction of dietary fat"
Again, that's the Ladybird Books version. While LCHF certainly does drive differences in insulin secretion, that's not an adequate explanation for bodyfat loss. It should be completely obvious that increasing the average power output from fat cells ("increased fat oxidation") does not necessarily result in a decrease in a body's average fat mass.
We selectively restricted dietary carbohydrate versus fat for 6 days following a 5-day baseline diet in 19 adults with obesity confined to a metabolic ward where they exercised daily.
Why? The authors seem dimly aware that the body is an adaptive system, and that it performs its adaptations fairly slowly (days). So what's the point of a 6-day study? They're watching an adaptation process. A blip, a transient. No information about the steady state can be gleaned from the results.
This single failure ensures that the experiment cannot answer any of the questions being posed in the introduction. It's such a huge, in-your-face failure that I'm just amazed that the paper was published.
The experimental diets were designed such that they were 30% lower in calories than the baseline diet
It's worth visualising what this looks like. The subjects came in weighing over 100kg and eating 2900kCal/day. That means they would be habituated to regular snacks and large meals. They're then switched down to 2000kCal/day. The immediate result is that they would be miserably hungry, both on low-fat and low-carb (if you're of normal bodyweight, imagine being put on 1400kCal/day).
In other words, the authors are studying something which would be impractical in real life; no fat person would be able to sustain it for more than a week without attempting to eat the wallpaper or their shoelaces. I suspect this is why the study was terminated at one week.
Apart from that, no real-world LCHF diet advocates forcible caloric restriction, so whatever metabolic response is observed is not the same metabolic response you'd observe on a normal LCHF diet.
Their "low carb" diet isn't even low carb; it's 140g/day, well above keto threshold, and nearly 30% of daily energy, which will reliably induce hunger and carb cravings. They do at least tell us why the decision was made:
Given the composition of the baseline diet, it was not possible to design an isocaloric very low-carbohydrate diet without also adding fat or protein. We decided against such an approach due to the difficulty in attributing any observed effects of the diet to the reduction in carbohydrate as opposed to the addition of fat or protein.
An admirable sentiment ("change as few things as possible") but completely misguided in this context. A low-carb diet must, of necessity, be high in fat. Otherwise it's just a restricted-calorie diet.
I won't bother going into all the results because given the above problems, they're essentially meaningless.
At the end of the discussion they more-or-less admit that the experiment was pointless:
Translation of our results to real-world weight-loss diets for treatment of obesity is limited since the experimental design and model simulations relied on strict control of food intake, which is unrealistic in free-living individuals. While our results suggest that the experimental reduced-fat diet was more effective at inducing body fat loss than the reduced-carbohydrate diet, diet adherence was strictly enforced. We did not address whether it would be easier to adhere to a reduced-fat or a reduced-carbohydrate diet under free-living conditions.
The results suggest no such thing, because you didn't even observe either a reduced-fat diet or a reduced carb diet. You observed six days' worth of moderate starvation. So why bother, guys? All you're doing is wasting funding that might be better spent elsewhere. But at least you got your names in Cell, and perhaps that's all that matters.
Ah, now I hadn't clicked through to the study itself, and I see what you mean. The article doesn't give enough away.
I thought a 14 day diet experiment was a bit too short, but 6 day diet is nonsense. It's a weird way to have participants cut out rather than replace - if you simply took my regular diet and cut back on 30% of the calories by getting me to avoid one of the macros, I'd think you were daft.
90% diet studies follow the same tired old paradigm: fiddle with one of the three macronutrients and see what happens. You'd think, after decades of doing that sort of thing, with nothing to show for it, they'd revise their approach!
People don't eat macronutrients - they eat food. So why don't dieticians study people eating actual food, instead of boiling things down into macros? To their credit they have actually started doing this - for example the paper that badger linked to - but there are still way too many of the other sort.
I think it's very unfair to judge the quality of a scientific paper on the basis of a radio report. We all know the press bowdlerise this stuff pretty badly.
I went looking for the paper, but didn't find it, but I found cell.com/cell-metabolism/fu... by the same author, and that seems to me to be stonking little study. They allowed a group of slightly overweight 30 somethings to free feed on either ultra processed food or unprocessed food nutrient matched for 14 days, and they ate 500 calories extra per day on the processed food, with no change to the amount of protein consume, and put on nearly a kg in 14 days.
Simple, clear and proof of what we know intuitively.
Strange this, coming from a US uni of such status and reputation, and with creditable links to Oxbridge. I think it's partly a matter of sloppy style and expression, poor punctuation, emotive language, clouded meaning etc, eg Susan Roberts professing (as Professor): 'I love this paper!'. Odd, and unprofessional. Unprofessorial, in fact.
In the States, all high school and uni teachers call themselves professor, which doesn't help, but I agree that it tells us very-little-to-nothing, in multiple single sentences.
From someone who is not from America but who has lived there (and has always worked in the education field) that is not true! Teachers are often referred to as “educators” or simply “ teachers” and those who teach at universities can only use the title “ Professor” if they have, in fact, a doctorate in the subject being taught. A great deal of tosh is still propounded on this side of the world re America — tosh that has never changed in 100 years.
Sorry but I've worked with American school teachers, all of whom called themselves Professor, though they all had PhDs, as have I, so I agree with you in part! I tried calling myself Professor for a while too but just in jest, which they took in good part
Roberts is an academic at Tuft's which, though not an Ivy League uni, has good connections with same and with Oxbridge. She contributes, or is reported to have done so, to commenting on a paper which is being reported on this popular science programme.
The problem with popular science is that it often devalues the currency of original research. I was showing surprise that she'd joined in, and her syntax is positively girlie.
But that's popular science. It has a function, but there's a price to pay.
Sorry, what? Girlie? I don't know whether it is feminine language or not, but to suggest you can't be a scientist and sound like a woman seems deeply sexist.
She loves the paper. At some point in an extended conversation with a reporter, she said so. I don't understand what the problem you have with that is.
In my industry, there's a running joke (yeah, we're not very funny people) called The International Obfuscated C Code Contest. The aim is to write a piece of code that does actually work while being utterly incomprehensible:
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The Politics of Diet