A more real world comparison is an electric bike commute. If the extra power for a cycle commute comes from human food then it's entirely possible that the extra carbon cost of making and charging the battery are a worthwhile investment to help save carbon footprint even though the bike is now heavier.

As you say, vegan vs carnivore (and red vs other meats) would be a factor just as whether the electric power comes from renewable or fossil power.

And to get super complicated you could then weigh the cost of healthcare if the rider is using less physical exertion.