Onion is a Green food. Green foods are safe to eat as a regular part of a diet.
Guideline related quotes related to Non-Starchy and Green throughout Geoff Bond's publications.
Eat at least 2 3/4 lbs of mixed salad and vegetables per day, consisting of "Green-Green” and “Green” foods. Of these, at least 3/4 lb should be mixed salad. Also include at least 5 cups of “Green-Green” leafy vegetables or 2 1/2 cups of other vegetables per week. ~Paleo in a Nutshell p.102
Specific references to Onion throughout Geoff Bond's publications.
Being a World War II baby, I spent the first fifteen years of my life on food rations. It is said that we are the "lucky" generation: Many unhealthy foods like sugar, bacon, pork, beef, milk, butter, fat, cakes, and even bread were strictly rationed. Meanwhile, we could eat as much as we liked of cabbage, onions, and turnips! ~Paleo in a Nutshell p.9
It is quite easy really to achieve six servings by eating one big salad every day with all the usual ingredients we think of as salad vegetables: Tomatoes, lettuce, radish, cucumber, mushrooms, onions, and so forth. ~Paleo in a Nutshell p.48
Conforming non-starchy, colored plant foods are foods that are low-glycemic, rich in micronutrients and fiber, and harmless with regard to anti-nutrients and antigens. Broadly, they include most salad foods, such as lettuce, onions, cucumber, radish, and mushrooms, and they also include colored vegetables, such as broccoli, green beans, bell peppers (sweet peppers), and Brussels sprouts. These are considered "Green-Green," "Green," and "Green-Amber." Under "Green-Green," we have separated out the vegetables that have the high concentrations of background micronutrients that our ancient ancestors delighted in. You can have unlimited consumption of these foods, and the ideal is up to two pounds (900 g) per day. ~Paleo in a Nutshell p.62
The idea of eating salad for breakfast does indeed run counter to our Western cultural programming, but it is something that many societies do, notably in Africa. A copious mixed salad with some avocado, tuna flakes, or shrimp makes a great start to the day. Again, make it a large portion— at least one pound per person. It is not really so much: One large tomato, one cucumber, some onion, and some lettuce leaves make 9 oz of plant food. Round it off with 3 oz of canned tuna, and you have a hearty breakfast. ~Paleo in a Nutshell p.87
Old-Fashioned Haddock Breakfast. This used to be a good standby in many parts of the English-speaking world. Many people are old enough to remember, perhaps, when their grandparents used to eat like this. They would lightly poach a piece of haddock (or kipper or any other appropriate fish) in simmering water for about five minutes. They would accompany it with lashings of sauteed onion, grilled tomatoes, and mushrooms. ~Paleo in a Nutshell p.88
"Fresh is best" is a familiar slogan and it is good for us, too. However, that is not always possible, so how do we prioritize? Broadly speaking, the "least bad" alternative to fresh plant food is frozen. Frozen plant foods, such as cauliflower, spinach, and chopped onion, have been quickly prepared in the field, and then blanched and frozen nearby. Blanching is designed to destroy certain enzymes that cause discoloration, softening, and bruising. It is likely that these are background micronutrients that are useful to the human body and become lost in the blanching process. So, here we make a compromise: In the absence of an alternative, freezing is the least of all evils. ~Paleo in a Nutshell p.92
The other methods of preserving plant food are to be avoided: Freeze-dried (packet soups), canned (peas, green beans), pickled in salt (gherkins), syruped (fruit jams and jellies), and fermented (sauerkraut). That is not to say you can never eat these things, just do not think that they are proper food. Foods pickled in vinegar (such as onions) have lost many nutrients, but at least the pickling does not add undesirable chemicals. ~Paleo in a Nutshell p.92
As biologist-historian Jared Diamond points out, only a few varieties of plants in the world lend themselves to being farmed and the farmer had little choice but to focus his efforts on those few. This practical reality greatly reduces the variety of foods eaten. So, it was for our first planters in Kurdistan. Instead of consuming plants from the hundreds of wild, foraged species, the farmers' diet was now limited mostly to just four farmed species— wheat, barley, lentils, and beans. As the centuries rolled by, farmers gradually domesticated some fruits (such as apricot and apple) and vegetables (such as onion and leeks), but they remained a tiny part of the diet. ~Deadly Harvest p.31
Not all underground vegetables are starchy. For example, turnip and radish, which both originated in Asia, are non-starchy, as are bulbs such as onion and garlic from Asia and the leek from the Middle East. Corms such as Chinese water chestnut are also non-starchy. Unlike the starchy roots, they mostly get their bulk from another com pound called "inulin." ~Deadly Harvest p.56
Foods pickled in vinegar (such as onions) have lost many nutrients, but at least the pickling does not add undesirable chemicals. ~Deadly Harvest p.166