4 ms·

The authors identify the fundamental limitation of their interpretation. To wit, you cannot be sure whether the improved biomarkers are a consequence of the dif

The authors identify the fundamental limitation of their interpretation. To wit, you cannot be sure whether the improved biomarkers are a consequence of the different contents of the diets or the bulk caloric differences: > Fifth, our study was not designed to be isocaloric; thus, changes to LDL-C cannot be separated from weight loss observed in the study.

MostlyStable 3y ago
Oh wow, I didn't get farther than how much meat they included to see that....that's a _very_ major methodological issue _especially_ when "weight loss" is one of the endpoints they tout!
- anonymouskimmer 3y ago
  As long as satiety is maintained enough to stay on the diet I don't see that it's necessarily an issue. Plants and nuts especially tend to be high in fiber and thus very filling per calorie. The mechanism of weight loss (lower caloric intake, here) isn't that important, as long as it's a sustainable mechanism.
  - MostlyStable 3y ago
    If the vegan participants were eating less on their own because the diet induced greater satiation, then great! That's a fantastic result. But these participants were provided meals from a meal service, so they were being presented with fewer calories. That's a very, very major problem, one that the authors themselves admit in the conclusions. Which is why it's frustrating to see them take such stronger language in the beginning of the article. They know it's an issue but pretend it isn't until the end when they hope that most people won't see it.
    - anonymouskimmer 3y ago
      > But these participants were provided meals from a meal service Only for the first month. And if it didn't satisfy them sufficiently study dropout or cheating would become more likely. They appear to have been allowed to 'cheat' formally, anyway. : Participants also purchased and consumed snacks to meet their energy requirements following guidance from health educators. : Although weight loss was not discouraged, our diet design did not include a prescribed energy restriction and was not intended to be a weight loss study. Participants were told to eat until they were satiated throughout the study. I'm more interested in their exclusion criteria, as this makes their study less generalizable to populations who may need it: : We excluded participants who weighed 45.36 kg (100 lb) or less, had a body mass index (calculated as weight in kilograms divided by height in meters squared) of 40 or higher, had an LDL-C level of 190 mg/dL or higher (to convert to millimoles per liter, multiply by 0.0259), had a systolic blood pressure of 160 mm Hg or higher or diastolic blood pressure of 90 mm Hg or higher, or were pregnant.
      - MostlyStable 3y ago
        >For the first month aka half of the entire study duration. As for "satisfaction" it didn't: diet satisfaction was reported lower in the vegan group. But while there may have been cheating, we know that the vegan group was consuming less calories, because they lost more weight. If they had been provided the same number of calories, that would tell us that they were cheating less or something similar. Because they were not though, we have no idea how much of it is due to some advantage of the diet vs. the difference in provided meals. The issue is not that this problem disproves advantages of a vegan diet. The problem is it makes it impossible to know. They have hopelessly confounded with a factor that we know is incredibly important in nutrition related health outcomes. And the authors know it too: >Fifth, our study was not designed to be isocaloric; thus, changes to LDL-C cannot be separated from weight loss observed in the study. I personally think that this one throw away sentence is far too small for what is probably the largest methodological issue in the study. Again, this problem doesn't disprove anything about vegan diets, it just makes it nearly impossible to learn anything from this study.
        anonymouskimmer 3y ago
        > If they had been provided the same number of calories, that would tell us that they were cheating less or something similar. They were specifically told to snack as needed. Given that they were told to eat until satisfied, and report that they were less satisfied, it seems that this study "proves" that the vegan diets used in this study are less satisfying than omnivorous diets, at least on average for a cohort who aren't used to vegan eating.

MostlyStable 3y ago

Oh wow, I didn't get farther than how much meat they included to see that....that's a _very_ major methodological issue _especially_ when "weight loss" is one of the endpoints they tout!

anonymouskimmer 3y ago
As long as satiety is maintained enough to stay on the diet I don't see that it's necessarily an issue. Plants and nuts especially tend to be high in fiber and thus very filling per calorie. The mechanism of weight loss (lower caloric intake, here) isn't that important, as long as it's a sustainable mechanism.
- MostlyStable 3y ago
  If the vegan participants were eating less on their own because the diet induced greater satiation, then great! That's a fantastic result. But these participants were provided meals from a meal service, so they were being presented with fewer calories. That's a very, very major problem, one that the authors themselves admit in the conclusions. Which is why it's frustrating to see them take such stronger language in the beginning of the article. They know it's an issue but pretend it isn't until the end when they hope that most people won't see it.
  - anonymouskimmer 3y ago
    > But these participants were provided meals from a meal service Only for the first month. And if it didn't satisfy them sufficiently study dropout or cheating would become more likely. They appear to have been allowed to 'cheat' formally, anyway. : Participants also purchased and consumed snacks to meet their energy requirements following guidance from health educators. : Although weight loss was not discouraged, our diet design did not include a prescribed energy restriction and was not intended to be a weight loss study. Participants were told to eat until they were satiated throughout the study. I'm more interested in their exclusion criteria, as this makes their study less generalizable to populations who may need it: : We excluded participants who weighed 45.36 kg (100 lb) or less, had a body mass index (calculated as weight in kilograms divided by height in meters squared) of 40 or higher, had an LDL-C level of 190 mg/dL or higher (to convert to millimoles per liter, multiply by 0.0259), had a systolic blood pressure of 160 mm Hg or higher or diastolic blood pressure of 90 mm Hg or higher, or were pregnant.
    - MostlyStable 3y ago
      >For the first month aka half of the entire study duration. As for "satisfaction" it didn't: diet satisfaction was reported lower in the vegan group. But while there may have been cheating, we know that the vegan group was consuming less calories, because they lost more weight. If they had been provided the same number of calories, that would tell us that they were cheating less or something similar. Because they were not though, we have no idea how much of it is due to some advantage of the diet vs. the difference in provided meals. The issue is not that this problem disproves advantages of a vegan diet. The problem is it makes it impossible to know. They have hopelessly confounded with a factor that we know is incredibly important in nutrition related health outcomes. And the authors know it too: >Fifth, our study was not designed to be isocaloric; thus, changes to LDL-C cannot be separated from weight loss observed in the study. I personally think that this one throw away sentence is far too small for what is probably the largest methodological issue in the study. Again, this problem doesn't disprove anything about vegan diets, it just makes it nearly impossible to learn anything from this study.
      - anonymouskimmer 3y ago
        > If they had been provided the same number of calories, that would tell us that they were cheating less or something similar. They were specifically told to snack as needed. Given that they were told to eat until satisfied, and report that they were less satisfied, it seems that this study "proves" that the vegan diets used in this study are less satisfying than omnivorous diets, at least on average for a cohort who aren't used to vegan eating.