Just a note about nitrates: apparently these are deadly only in meat, for some reason, because the people who want us to stop eating meat have no problem with eating much larger quantities of nitrates in their favourite plants. I wonder how the nitrates know to make trouble only when they find themselves in meat? 
And my more general comment on the thread: we usually talk as though there is only one form of weight gain or loss when the scale number changes (or doesn’t, as the case may be), forgetting that body weight is actually what Jason Fung calls a “two-compartment problem.” In other words, weight comprises both lean mass and fat mass, and which compartment is going to be affected by changes in our diet is primarily the result of the body’s hormonal response to what we eat, far more than the quantity we eat.
There are nearly a dozen different hormones involved directly in metabolic function and regulation and others indirectly. It’s all about energy management - what comes in, what happens to it and what goes out or not. If any of the hormones involved managing energy throughput isn’t doing it’s specific job efficiently (or at all), the whole system suffers. We’re not a lab calorimeter, so energy is not a simple in/out measurement.
I mentioned above that I suspect I inherited my dad’s active thyroid before it went hyper and I think that saved me from decades eating SAD. Until the decade of my 60s, then I started to gain weight. Slowly enough not to become a big issue, but steadily. By the time I started keto at the age of 71, I carried about 30-35 pounds of excess. I now interpret that as gradual insulin resistance which is the inevitable result of SAD combined with thyroid slowdown due to age. So, yes, 60 changes lots of things!