I suspect it's because the diet eliminates some foods that I'm allergic/sensitive to (how could it not with how many foods it necessitates cutting out?), so the causation might not actually be the low carb diet, as some vegans claim a similar result. In that context it stands to reason that both sets of dieters are finding existing sensitivities and chalking up the gains to the diet. I found out that for me glutamate, both from natural and artificial sources, causes substantial headaches, which is a bummer because I love bone broth. Beans also give me restless legs at night.

So while it's hard to be absolutely scientific in your everyday life, it doesn't mean it's impossible to glean any sort of improvement in your health and well-being through personal experimentation.