Complicated question, which leads to several other research areas.

Firstly, what is the average carbon footprint of a calorie? You could then do an analysis of the average cycle commute and calculate its carbon footprint, plus the cost of making the bike and all that lycra that is being worn. Add to that the batteries and other electrics in the lights being worn. Compare and contrast against the carbon footprint of the average car and its commute journey.

Next up, and to complicate things, we would need to examine the eating habits of the nation. I seem to recall reading a few headlines of late proclaiming that we are all obese - hence we are all already eating too many calories. The question would need to be asked "would we eat yet more calories if we were all forced to cycle to work (where appropriate)?". If the answer is "no", then the calorie difference between cycling and driving would be zero, hence there would be no differential in that aspect of the commuting carbon footprint. We would then, of course, all become svelte cycling athletes, rather than the overweight lot that we are.

In your calculations, you would of course have to consider the carbon footprint of transporting the petrol to your car, as well as the footprint of burning it - similarly to counting the cost of transporting the calories to you to eat so that you can cycle. My daily commute is 20 miles round trip, usually at 30 mpg. So I use 2/3 of a gallon daily. This would weight around at least 3kg. I don't think I'd eat 3kg of food if I cycled (although I'd need a fair amount more!).

I'm sure there are more calculation tangents that could be explored

I think you are possibly quite correct. Which is why I am moving myself and my family into the Cadbury's factory. We are going to home-educate my daughter in the art of confectionary, and eat nothing but Cadbury's creme eggs, taken from the production line before they are wrapped in foil. I intend to work as a quality assurance technician for the company.

Despite being at the apex of my boffinness, it's not a study I've conducted myself.