A couple important points to add some clarity. First, penmypaper is not in the least a reliable source of information – it is a paper-writing mill for students looking to cheat. For reliable sources of information, it is necessary to go straight to the research articles themselves. Second, based on the misguided source of information, there seems to be a misunderstanding by Cadmium what a plant-based diet is. It is not simply a pile of vegetables or fruit on a plate, but includes all plant-sourced foods including whole grains, seeds, nuts, pulses, legumes and more. Energy density is not an issue.
A proper, diversified plant-based diet, based on whole-foods, can easily meet the nutritional and energy demands of any outdoor athlete, but any healthy diet, whether flexitarian, vegetarian or vegan, requires some forethought and effort. A risk for some people switching to a mostly or all plant-based diet is that this is done solely by reducing/eliminating meat, dairy and/or eggs, rather than thinking about it holistically. There is quite a bit of research on vegan and vegetarian diets within sports science, which shows no negatives and possibly benefits (for example, the ongoing NURMI study, with several recent papers by Wirnitzer and co-workers), and more broadly within epidemiology that shows positive effects particularly regarding cardiovascular disease. There are also good reviews addressing macro- and micronutrient issues for vegan/vegetarian athletes (for example, Fuhrman and Ferreri, 2010, in Current Sports Medicine Reports), where, for example, B12 can be a concern requiring supplements. Game Changers has a lot of merits, I think they represented the science fairly well, but it is short on ‘how to’, so if you are unsure where to start, then having a discussion with a dietician/nutritionist could be a useful starting point, as suggested.
One person’s experience is only anecdotal, so the only personal note I will make is that I am in my late-50’s and have been vegan for more than six years, and it has not impacted my ability to sustain a training habit of 10+ hours per week and run ultras when I occasionally decide to. In all honesty it is impossible to state objectively whether I recover faster, have less inflammation, etc. – I have no reference ‘me’ to compare to. It is only fair to say I can train a lot and diet is not a limiting factor. With that switch I did and still do spend a great deal of time reading the research literature out of personal interest, and spend more time and effort cooking; more plants in the diet means more time at the cutting board, but also opened the door to seeking out new foods and new recipes. Importantly, by your description at the start of this thread, your current diet is not working so well, so there is only going forwards – and I wish you luck in your progress.