And, second: increasing overall availability of energy in the body can make infections and cancers worse.

I wonder about this. A lot of things, including cancers, are caused by viruses / may be caused by undiscovered infective agents. If slow metabolism also slows your immune system, then a lot of horrid things might take advantage of that fact.

Cochran said that on genetic load grounds alone, we should expect an awful lot of diseases we currently think are non-infective to be cryptically infective (e.g. ulcers) or recent broken infection defenses (e.g. sickle-cell).