It means that the natural food industry is facing a massively constrained optimisation problem.
Define "massively"?
To the best of my (admittedly relatively ignorant) knowledge:
The worst generally acknowledged culprits for dietary promotion of disease are sugars and trans fats. Sugars are easy to add in arbitrary quantities in "all natural" form.
The worst remaining likely culprits for dietary promotion of disease are salt, nitrates/nitrites, and excesses of many other fats (likely everything except omega-3 and monounsaturated fatty acids in the average modern diet?). These are all easy to add via "all natural" ingredients.
The worst still-controversial suspected culprits for dietary promotion of disease are high-carb diets and high dietary cholesterol; both of these are easy to add via "all natural" sources.
We obviously don't know nearly as much as we should about nutrition as we should. The big Mediterranean diet study showing 50+% reduction in cardiovascular incidents was only a decade ago, and the study narrowing most of that down to nuts and olive oil was just a year ago! But it seems that we know enough to say that there are ways to make food much more immediately satisfying and much less healthy without using any ingredients that wouldn't have been available throughout human history; all we have to do is use too much of some of them. All-natural diets scored a big victory in the case of trans fats, and may avoid similar artificial food mistakes in the future too, but the worst natural ingredients seem to be much worse for you than the best artificial ingredients, so simply avoiding the latter isn't a panacea.
A look at all natural foods through the lenses of Bayesianism, optimisation, and friendly utility functions.
How should we consider foods that claim to be "all natural"? Or, since that claim is a cheap signal, foods that have few ingredients, all of them easy to recognise and all "natural"? Or "GM free"?
From the logical point of view, the case is clear: valuing these foods is nothing more that the appeal to nature fallacy. Natural products include many pernicious things (such as tobacco, hemlock, belladonna, countless parasites, etc...). And the difference between natural and not-natural isn't obvious: synthetic vitamin C is identical to the "natural" molecule, and gene modifications are just advanced forms of selective breeding.
But we're not just logicians, we're Bayesians. So let's make a few prior assumptions:
Now let's see the food industry as optimising along a few axis:
The last point is the weakest one, though. Long term health impacts are fiendishly hard to measure (by anyone), and consumers' memories are short. The main things that the food industry wants to avoid are blaring headlines like "salmon saturated with mercury", "sugar linked to cancer", or "food industry coverup". Even there, journalists can create scandals out of very little (or ignore major ones if something more juicy comes along), so the pressure to actually prioritise long term consumer health is very weak. So most optimisation pressure is along the first two axis.
So the food industry will strongly push to decrease cost and increase satisfaction, while mostly taking a random walk on long term consumer health. Given the assumptions above, this means that we'd expect the long term health impacts to worsen (because there are far more negative products than good one). This somewhat similar to the importance of programming everything of value into a friendly AI, lest the things not programmed get squeezed out.
Now, what does "all natural" mean in this setting? It means that the natural food industry is facing a massively constrained optimisation problem. They are extremely limited in what they can do (compared with the rest of the industry), and it mostly involves shuffling around with products we suspect to be benign or positive. Similarly with GM modifications: selective breeding is much slower and uncertain, so the optimisation pressure is less: they literally can't change things as much or as fast. One supporting argument for this is that all natural or GM-free products tend to be more expensive or less satisfying than others, demonstrating less optimisation pressure.
This is entirely not a result I expected to find. Pushing it to the extreme, it would seem that the most traditional and unchanged food (after removing stuff we know to be bad) is likely to be best, as long as people don't get too inventive with them.