Whether correcting deficiencies with whole foods alone is possible depends on many factors: how bad the deficiencies are, which minerals are deficient, your health status, environmental conditions, etc. For example, if you live in an area with selenium-poor soils, and that’s your only deficiency, then eating whole foods that contain selenium should be enough. But if you’re unhealthy and have a number of deficiencies that have advanced to the point where your ability to absorb nutrients from your food is impaired, then food alone may not be enough.

There are things you can do to improve how well nutrients are absorbed from your food. As I’ve mentioned before, chewing really well is an important one. Eating a good variety of food is another (avoid a mono-diet). Juicing (veggie juices) can also help.

I tried a whole food approach for quite a while, without supplementation, and it wasn’t enough for me–but I was very unwell at the time. I had to add supplements before I started to make any progress. In fact, after everything corrected, I stopped taking supplements and went back to whole foods only, and found that several minerals in my blood dropped back down well below normal. So for me, I need to continue certain supplements even today.

One issue with using whole foods alone is that there can be considerable
variation in the mineral content of your food. Also, certain types of food are good sources for certain minerals; if you eliminate those foods from your diet, it can be a challenge to get enough of the associated minerals. For example, molybdenum is present in beans; if you don’t eat beans, it can be difficult to get enough.

Of course, if you’re healthy and live in good environment, I don’t think
this is an issue. Paleo people certainly didn’t need supplements to survive and thrive.

I suspect that glutathione (GSH) deficiency is relatively common in modern society. Although the body will create GSH, it needs the sulphur-containing amino acid cysteine in order to do so. Unfortunately, sulphur intake, including cysteine, tends to be fairly low with modern diets. Since GSH is involved with many detoxification reactions, it also gets consumed much more quickly now than in the past, given our regular exposure to things like pesticides.

In addition, in order for GSH to be used properly by the body, the mineral selenium (Se) is required. Se is present in GSH peroxidase, one function of which is to eliminate peroxides such as hydrogen peroxide. Se is also often low in the diet, particularly in certain regions with soils that are naturally low in Se, such as Finland and New Zealand. Low levels of Se in the blood are a well-documented risk factor for cancer.

Just because the chemical pathways exist in the body doesn’t mean that nutrients or their co-factors are being made in the quantity needed. Also, supplementation of the substance itself (such as GSH, which is largely destroyed in the stomach) is often not the best way to address the problem; specific precursors such as cysteine or Se may be much more effective. Getting these precursors through diet is the ideal for the long-term, diet alone may not be enough to correct or even prevent deficiencies (depending on where you live and the source and quality of your food).