It’s hard to find “real downsides”. Theoretically it can lead to bloating and weight gain, but these are super-reversible side effects. What i"m most interested is in the non-reversible side effects
I think the most concerning ones come from ingestion of excess microplastics or (possibly) indigestible tannins/waxes that may also get stuck inside cells…
Often I eat more vegetables than all the rest of the 50 people at an event combined
Relevance of Diabetic Retinopathy with AGEs and Carotenoid Levels Assessed by Skin Sensors - PMC has something, but “very frequent/high intake” isn’t even comparable with the levels of vegetables I eat each day…
The forced-choice scale with a 4-point rating system was used to estimate the amount of vegetable intake, in which a vegetable intake score of 0 indicated no or rare intake, (1) sometimes/small amount, (2) frequent/sufficient amount, and (3) very frequent/high intake
The study did not find a difference in Veggie scores among the control, NDR, and DR groups, whereas female sex, nonsmoking status, and better BCVA were associated with higher Veggie scores (Table 10). Higher carotenoid levels in women and nonsmoking status have been reported previously [19,20,21]. Higher dietary intake of carotenoids in women than men has also been reported ; thus, the current results are consistent with previous studies. The Veggie score clearly reflected the vegetable intake score (Table 8). Collectively, the results suggest that the fingertip measurement appropriately estimated the carotenoid levels. Provitamin A carotenoids, which are converted into vitamin A, are essential for maintaining the photoreceptor cell function. Macular pigment xanthophylls, such as lutein and zeaxanthin, are the major protectants of the foveal region via their antiphotooxidative stress effects . Filtering of the harmful shorter wavelength blue light and/or elimination of singlet oxygen species explains the cellular protection activities of these macular pigment carotenoids . Carotenoids were associated with better visual function by maintaining lens transparency  and macular function . Considering these previous findings, the relationship between better BCVA and Veggie scores detected in this study (Table 5 and Table 10) seems reasonable. Contrary to expectations, higher Veggie scores were associated with higher DR risk (Table 3). More aggressive or rigorous dietary guidance applied to patients with DM/DR compared with controls might explain this result, although this needs to be tested.