Antioxidant foods are foods which provide chemicals which act to repair or prevent oxidative damage in the body. Fruits and vegetables are marketed as health foods because they are high in antioxidants and phytonutrients, other plant based chemicals which are believed to also have health benefits.
I mention them because a reader wrote to me and asked how one's body "gets all the vitamins, minerals, enzymes, antioxidants and other necessary phytonutrients it needs when nutritious whole carbs such as raw fruit and high glycemic veggies are eliminated or severely restricted" on a ketogenic diet.
It's a good question, and I wanted to address it because I'm sure others have the same question.
On my facts about vitamins page, I explain that animal based foods are higher in most vitamins and minerals than plant based foods on a 1 cup serving basis. Only vitamin K, vitamin C and vitamin E are higher in plant foods, hence the recommendation to eats lots of green leafy vegetables and nuts on a ketogenic diet. Vegetables are chock full of vitamin K and C, and nuts are high in vitamin E.
And one of the most potent antioxidants in the body is an amino acid called glutathione. The body makes it from several other sulfur amino acids, (the main building units of proteins).
There are many foods which boost glutathione production. Asparagus, broccoli, avocado, spinach, eggs, garlic and fresh unprocessed meats contain high levels of sulphur-containing amino acids and help to maintain optimal glutathione levels.
In addition, un-denatured whey protein isolate powder contains proteins which are high in sulphur-containing amino acids.
Vitamin C is in particular a hot topic in relation to a low carb diet because fruit is high in vitamin C, and it is restricted on a low carb, ketogenic diet. I explain here why less vitamin C is needed when one eats a low carb diet, and highlight the fact that since animals make their own vitamin c internally, it is present in animal based foods.
As for the antioxidants deficiency issue, I'll point out that there is little convincing evidence that the antioxidants in fruits and vegetables extend life and health.
The Women's Health Initiative Study results, which were published in the Journal of the American Medical Association in 2006, clearly showed that over time, a dietary intervention that reduced total fat intake and increased intakes of antioxidant foods such as vegetables and fruits did NOT significantly reduce the risk of CHD, stroke, or CVD.
In addition, the recent hype about phytonutrients fails to mention that these plant based chemicals are not essential nutrients, (except for the companies making phytonutrient supplements) and in fact, some studies have shown that fruit and vegetable consumption is in fact not protective, and can actually be more harmful than helpful.
Although designed to look at green tea antioxidant efficacy, (which was nil) the authors of the study mentioned above wrote that the study "essentially served as a fruit and vegetables depletion study. The overall effect of the 10-week period without dietary fruits and vegetables was a DECREASE in oxidative damage to DNA, blood proteins, and plasma lipids, concomitantly with marked changes in antioxidative defence."
In other words, removing fruits and vegetables from the diet was actually better for the study participant's overall health.
And antioxidant supplements are not so great for health either. Newsweek published an article title "Anti-oxidants Fall from Grace" in which they discuss a meta-analysis done by the prestigious Cochrane Collaboration on the health benefits of antioxidant supplements:
"In 2008, the Cochrane Collaboration, an international consortium of scientists who assess medical research, scrutinized 67 studies with nearly 400,000 participants. The goal: to determine whether antioxidant supplements reduce mortality in either healthy people or in people with cardiovascular, neurological, rheumatoid, renal, endocrine, or other diseases. Conclusion: “We found no evidence to support antioxidant supplements for primary or secondary prevention, [and] Vitamin A, beta-carotene, and vitamin E may increase mortality.” In analyses of antioxidant supplements and Lou Gehrig’s disease, Alzheimer’s or mild cognitive impairment, and lung cancer, the Cochrane scientists’ verdict was the same: no, no, no, and no. And each analysis had an alarming refrain about increasing overall mortality."
You can read the entire article here.
In addition, Peter Dobromylskyj over at the Hyperlipid blog has an interesting post on this idea and he lists several more studies which show that consuming antioxidant foods such as fruit and vegetables INCREASES oxidative stress markers.
In conclusion, the common consensus that consuming more fruits and vegetables and other antioxidant foods correlates to greater health is not based on solid evidence. If you still have questions, I highly recommend reading this post by Dr. Art Ayers.
You can also watch this video from Dr. Georgia Ede:
Finally, a ketogenic diet does restrict antioxidant foods such as fruits and starchy vegetables, with the goal of resolving weight and health problems.
The point of a ketogenic diet is to modify carbohydrate intake until health and weight issues are addressed, and then to stick to a carbohydrate intake level that maintains this new and better state of health.
If your weight is normal and you can tolerate the carbs in fruits and starchy vegetables without metabolic issues, there's no reason you can't eat them in moderation.
However, most people with weight problems and metabolic syndrome issues are "carb sensitive" and they cannot handle eating these foods without blood sugar issues and weight gain.
Hence, a ketogenic diet which restricts these high carb antioxidant foods is most helpful to them.