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I've read this article online in a Belgian newspaper (in Dutch): Weet wat je zweet: deze 7 dingen wist je nog niet over zweten — HLN.

Number 4 is saying that vegetarian sweat smells better then non vegetarian sweat.

I've done some research and found this article: Do Vegetarians Smell Sexier? — Psychology Today.

That article refers to 2 studies. One study found that:

As you can see in this graph, women rated the body odors of the men to be sexier, more pleasant, and less intense after they had given up meat for two weeks. The experiment worked. Who knew?

And the other:

But in contrast to results of the Czech study, the Australian women rated the body odors of frequent meat eaters to be more pleasant than men who ate a lot of vegetables. No one knows why the two groups of researchers obtained opposite results when in comes to how meat-eating affects body odor.

So do vegetarians and their sweat smell better?

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    Do these studies indicate what types of food the vegetarians were eating? Stinky foods like onions and garlic usually make your sweat smell worse. – awells Jul 26 '18 at 13:26
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    Do they smell better to who? The chemicals making up a smell are objective, but the evaluation of that smell as being good or bad is subjective. Both of the studies you mention could be accurate because they're asking for preferences in different populations. – combinatorics Jul 26 '18 at 14:00
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    I have no doubt that carnivores think that vegetarians smell better. – Michael J. Jul 26 '18 at 16:46
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    @DavidHammen: And in this particular case it is proven to be influenced by the current phase of the woman's hormonal cycle. – David Foerster Jul 26 '18 at 22:26
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    @Zeus If that published research finding is true then it logically follows that it itself is probably false in which case it is probably true. – Vince O'Sullivan Jul 27 '18 at 9:05
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"Smell" is a sense that is said to be more directly tied to emotional processing in the brain than other senses. But all interpretations of sensory information is subject to subjectivity. And smell is a sense that is easily and quickly dulled. Live in the stink and you get used to it, quickly.

That makes it this a

No. Smell is not objectively measurable as "better". Vegetarians do smell different, but the overall effect of just meat-eating is quite small.

As such "better smell" is not the most reasonable category to begin with. Human body odour varies with genetics, hormonal status changes, diet (as this includes drug use: meaning any substance consumption and the consequent metabolism) and other environmental factors, to which I would count availability of water and soap, usage pattern of both and the interaction of all of that with the skin microbiome.

In most circumstances the sweat of healthy individuals does not smell that much at all. It's after the bacteria on the skin metabolise components of that sweat that most often rated as unpleasant smells develop.

That means "better smell" is hard to define and of all influencing factors only the diet part has to be examined. That is doable if "better smell" is defined at systematically and significantly different between meat eaters and vegetarians.

Individual and gender fingerprints in human body odour
Environmental Effects on Human Body Odour
Does Personality Smell? Accuracy of Personality Assessments Based on Body Odour

Going by the Czech study
Jan Havlicek & Pavlina Lenochova: "The Effect of Meat Consumption on Body Odor Attractiveness", Chemical Senses, Volume 31, Issue 8, 1 October 2006, Pages 747–752: they set up a big controlling scheme to focus on diet:

They were instructed to refrain from 1) using perfumes, deodorants, antiperspirants, aftershave, and shower gels, 2) eating meals containing garlic, onion, chilli, pepper, vinegar, blue cheese, cabbage, radish, fermented milk products, and marinated fish, 3) drinking alcoholic beverages or using other drugs, and 4) smoking. As this very strict procedure had to be maintained for a relatively long period, during the first stage (days 1–10), nonserious violations were tolerated (e.g., one 0.5l beer or one glass of wine).

That means first: in an almost laboratory setting that unrealistically excluded most of the fun from both diets there was a measurable difference between odours that raters were able to detect (and categorise according to the wishes of the experimenter into a pleasant–unpleasant scale.)

Curiously, they did not control for different types of red meat, since nitrate and nitrite preservatives (so called nitro meat) are now widely used to achieve redness of the product. If that is not checked for, then we have zero info on how very fresh meat or traditionally prepared red meat (i.e. Italian parma ham is just salted and aged pork, no nitro salts added), meaning in this study humans might have been shown to detect in body odour just whether or how much nitro-compounds the participants consumed.

This one study exemplifies quite a lot of limitations to the interpretation of its results. Overall protein content, amino acid composition, fatty acid composition etc were apparently not well controlled.
From a chemical analysis perspective they should really have asked themselves beforehand what exactly differentiates meat and therefore a meat-diet from a vegan diet and its components. Was the meat "organically" produced or due to funding reasons the cheap variety, of which conventional wisdom might suspect that it is full of hormones, anti-biotics, effects of stress on the animals like unnatural feeding patterns (i.e. corn based cow diet vs grass fed)?

Meat consumption is one small part of body odour composition. As the study designers seem to know by excluding for example the much more dominant garlic smell. Eat no meat but a lot of garlic and most people will likely report the effects as unpleasant. Give these 'most people' the same amount of garlic and they will not notice that much of a difference compared to themselves.

Jane L. Hurst et al.: "Chemical Signals in Vertebrates 11", Springer: New York, 2007. Chapters: Ecological Validity in the Study of Human Pheromones, The Influence of Sexual Orientation on Human Olfactory Function, Human Body Odour Individuality, Environmental Effects on Human Body Odour, The Effect of Familiarity on Mate Choice,

Meat as such might mean you have a protein rich diet, lots of sulphur compounds like certain amino acids in it as well as certain fatty acids not so easily found in vegetables.

But all of this pales in comparison with cultural factors, group awareness, and other habits:

Prior to World War II, Japanese contact with the West had been at a minimum. When they came in contact with the Portuguese in the sixteenth century and the more numerous English and Americans in the 19th century, they reacted with shock. The blue eyes and “red” hair of westerners are attributes of goblins in Japanese folklore. They were appalled at the hairy, sweaty bodies that gave off a strong body odor due to a diet higher in animal fat. Those who did meet Europeans were disgusted by their stench: people who seldom touch animal products are extremely sensitive to the body-odor exuded by eaters of animal fat.
It was butter, the Japanese thought, which made Europeans so peculiarly rank: bata-kusai they called them (using the English word for the foul substance): “butter-stinkers." The terms Bata-kusai, “stinking of butter,” is still a derogatory term for things obnoxiously Western.
From Butter in Japan, compare to Wasei ego. Not exactly loan words

The cultural norms that prevail or are being introduced are far stronger than anything objectively measurable with chemical sensors:

Daniel M.T Fessler: "Disgust sensitivity and meat consumption: a test of an emotivist account of moral vegetarianism", Appetite Volume 41, Issue 1, August 2003, Pages 31-41.
We conclude that moral vegetarianism conforms to traditional explanations of moral reasoning, i.e. moral vegetarians’ disgust reactions to meat are caused by, rather than causal of, their moral beliefs.

And this preference reflects back into the body odour department

More Than Meets The Nose All that said, though, the study’s findings seemingly haven’t been repeated by anyone else. And you don’t have to look too hard to find people complaining about their odoriferous emissions following a switch to a vegetarian diet — asparagus being one of the chief culprits. In both cases, it’s likely the higher levels of chemicals that are eventually broken down into sulfur that further explains the pungent smell. Still, unless you’re switching from an everyday diet of meat hoagies to fresh garden greens, the differences in body odor will likely be marginal, especially if you’re taking regular showers.
That’s not to say that eating meat isn’t bad for your dating pool. A 2007 survey out of New Zealand found that most vegans, especially women, were less than receptive to the idea of dating carnivores. And some certainly cited fouler-smelling odors and bodily fluids as a chief reason why. Given how selective vegans are about their lifestyle choices, though, the researchers suggested that at least some of the disdain was simply because meat eaters didn’t share their ideological beliefs.
It’s just as well — no one should date someone that they have to constantly hold their noses in front of, whether physically or philosophically.
Ed cara: "Do Meat Eaters Really Smell Worse Than Vegetarians?", Medical Daily, Sep 6, 2016.

Just a funny side note: As with most things the dose makes the poison, rendering the broad "better" claim much too simplistic and extra dubious. Consider skatole

has a strong fecal odor. In low concentrations, it has a flowery smell and is found in several flowers and essential oils, including those of orange blossoms, jasmine, and Ziziphus mauritiana. It is used as a fragrance and fixative in many perfumes and as an aroma compound. Its name is derived from the Greek root skato- meaning "feces".

Conclusion

You are what you eat, and you certainly will smell a bit like that. We do not need dog noses to smell a difference between the effects of radically different diets. But "better smell" is not really a useful characterisation for the effect of eliminating only meat from a diet.

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    -1, just because something is subjective does not mean we can't attempt to objectively measure it (see: all of psychology) – BlueRaja - Danny Pflughoeft Jul 26 '18 at 16:42
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    @BlueRaja-DannyPflughoeft Only if we can come up with an objective measure that's consistent. Like how much different a behavior pattern is from the norm, or how bad a symptom of an issue is (e.g. how frequent a twitch is, etc). Notably, it has to be at least a little consistent - with the same input, most people should come to the same result. It's like asking "which is objectively better, blonde hair or brown hair?" Some people like one, and others like the other. We can objectively measure the colors but we can't objectively measure the "betterness" of either. – Delioth Jul 26 '18 at 17:15
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    @BlueRaja-DannyPflughoeft Your statement may be a non sequitur for criticising the answer and seems to conflate objectivity and intersubjectivty? or inter-rater reliability? – LangLangC Jul 26 '18 at 18:06
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    @Delioth thats because there is no good or bad hair color, but there are a lot of good and bad smells, like the small of your favorite food, or a fart? of course most people would choose their favorite food smells. – montelof Jul 26 '18 at 23:05
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    @LangLangC Might want to add this to your answer; many East Asians (including Japanese) genetically have less body odor. More info about ABCC11 here. It is fairly obvious to me that having this gene is more important for determining an individual's odor levels than meat consumption. – axsvl77 Jul 29 '18 at 2:37

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