Good question - and of course neither I nor metabolic theory are suggesting that genes do not matter - Genes are certainly involved in inheritance and passing on of information without a doubt.

However, the suggestion from myself and from metabolic theory is that, though genes may pass on information from one generation to the next, it is the environment, including our food, stress levels, and living conditions, which determines our health, and also that a life lived with plenty of energy and good environment can pass changes down to our offspring in both a genetic and non genetic way.

This is actually a common misconception - The Neo-Darwinists managed to change the way many of us now understand Darwins natural selection - but in fact Drawin himself was a confirmed "Lamarckist", which you can find well documented in various places including here - academic.oup.com/ije/article/45/6/2206/2617243

So my basic understanding is that they are both essentially states of lower energy availability, and that one of them is perhaps more advanced than the other. This is where we might say that your genes come into the picture - yes you might have what we could call a "genetic" predisposition to depression, in that perhaps your brain is not functioning as optimally as in a "healthy" person, but it is still very much your environment and energy which determine whether or not you ever get depression, and, conversely, increasing your energy stores and use can cure the depression.

For someone with cancer metabolic theory would suggest that the energetic deficit is simply far greater, to the point of which the cells involved are so starved of energy that they have had to dismantle their structure in order to survive...but it has been shown that even cancer cells can become normal cells again given enough energy.

haidut.me/?p=1668

Well...not exactly...They are both related in the sense of both being "low energy" problems, but you would work with them differently depending on your current circumstances, individual history, and context.

Both of them might benefit from large amounts of the b vitamins which are heavily involved in restoring proper energy for instance, but whilst low libido might just require a dietary shift and looking at macronutrients and fat soluble vitamins, cancer might require a much stronger approach using protective hormones, thyroid, and other regenerative substances.