The O2 Diet

Medically Reviewed by Christine Mikstas, RD, LD on June 06, 2023
Written by Lisa Schweitzer
4 min read

Could you slow down aging, get more energy, and lose weight, too -- without counting calories or sacrificing taste?

The O2 diet, by registered dietitian Keri Glassman, says you can.

Glassman’s 32-day plan centers on the ORAC (oxygen radical absorbance capacity) scale, which tells you how rich a food is in antioxidants. The higher the ORAC score, the better.

On this plan, you count ORAC points, not calories. You eat more of the ORAC scale’s top-rated foods, including leafy greens, artichokes, blueberries, salmon, herbs, and spices and less of the lowest, such as fried foods, baked goods, candy, and soda.

You eat three meals and at least one snack a day.

Off-limits: fried foods, baked goods, sugar- and fat-free processed foods, high-fat or processed meats, soda, artificial sweeteners, trans fats, and high-fructose corn syrup.

The first few weeks of the plan can be fairly intense, particularly the first few days.

Phase 1 (lasts 4 days): This phase is a "cleanse." You get a whopping 50,000 ORAC points per day on very few calories, and you drink water and green tea.

Phase 2: You get 30,000 ORAC points a day, control your portions, and eat lots of fresh fruits and veggies for 2 weeks.

Phase 3: You can add one indulgence per week, and you get more food options. This phase lasts for 2 weeks.

Phase 4 (ongoing): Stick with the Phase 3 guidelines, plus one more indulgence per week and one more high-ORAC fruit per day.

You can't have alcohol during Phases 1 and 2. You can drink, in moderation, in Phases 3 and 4, as one of your indulgences.

You may have to make a big change in your food choices, depending on what you eat now. But this change is meant to last.

Limitations: You have more restrictions at the start of the plan, but they loosen up.

Cooking and shopping: You should be able to find many ORAC-rich foods at your grocery store. The book includes tips for eating out and choosing foods at convenience stores.

Packaged foods or meals: No.

In-person meetings: No.

Exercise: Every week, you should do 2.5 hours of moderate exercise.

You can easily adjust this plan to fit vegetarian, vegan, and gluten-free needs.

Cost: Just your groceries.

Support: You do this plan on your own. Glassman's website includes recipes.

Does It Work?

The heart of the O2 Diet is the ORAC scale, which was developed years ago by the USDA to show how rich a food is in antioxidants.

In 2012, the USDA removed this table from their web site due to concerns that it had been misunderstood and misused. The USDA says that the ORAC rating is a scientific reference tool and that there is no proof that number has any relevance to human health.

Claims that these foods will slow down aging or give you more energy are unproven. But since the diet is packed with healthy fruits and vegetables and restricts calories, it will probably help you lose weight.

Is it Good for Certain Conditions?

If you are overweight, any weight loss will help lower blood pressure and prevent heart disease. By avoiding the off-limits foods, which include fried foods, high-fat or processed meats, and trans fats, you will be helping to keep your cholesterol level in line.

The exercise portion of the O2 Diet is in line with the recommendations that everyone should aim for 150 minutes of moderate exercise each week.

Exercise along with the weight loss is a proven strategy to help prevent diabetes. If you already have diabetes, you will need to change your treatment plan to accommodate the cut in calories and the boost in activity. Make sure you talk with your doctor first.

The Final Word

There’s no proof that the O2 Diet works any better or differently than any other very low calorie diet for weight loss, or that any fresh fruit or vegetable is somehow better than any others.

But the now-discredited ORAC list is ripe with some very healthy food choices, and the plan is easy to follow.

You have to be willing to shop and cook to follow this diet.  Tips for eating out are included in the plan, though this may be tricky to do.

Depending on your eating habits, you will likely have to be a bit more adventurous to follow the plan. And you will have to be highly motivated to stick with it, especially during the 4-day cleanse phase.