How Not to Age: An In-Depth Review

Exploring the Strengths and Weaknesses of Dr. Greger’s Anti-Aging Approach

How Not to Age cover

Dr. Greger is confident that plant-based foods can cure any human ailment. After writing two best-selling books on the same topic, he has released a third book. While previously he may have heeded advice that shorter is better, he now grumbles about his publisher’s 600-page length limitation. Instead of cutting more, he moved the citations online, removed the page breaks between chapters, and excluded the conclusion and index from the page limit.

Dr. Greger has published a lot, and he attempts to reference all his writings, podcasts, and videos in this book. There are almost 70 references to his previous How Not to Diet and How Not to Die books. Referencing his other books still misses his online content, so he also sprinkles over 400 URLs to YouTube videos throughout the book.

The online content links are distracting. Many lead to a verbatim copy of the book content, while others are irrelevant because he’s already said in the book that the proposed treatment doesn’t work. Some lead you to open the link by mentioning interventions but require you to go online to learn if they are safe and effective.

Is There an Editor in the House?

In his effort to include all knowledge about plant diets, he often includes esoteric information that could have been omitted, such as mentioning obscure Chinese medicines (Astragalus? Gotu Kola?) only to conclude that tests showed no significant effect. One sidebar discusses essential tremors potentially related to meat consumption and notes that marinating camel meat in strawberry juice for over 24 hours could reduce the damage by 40%. Camel meat seems unlikely to be a common cause of hand tremors in the Western world.

In his effort to lay out everything he knows about nutrition and aging, How Not to Age loses focus. He outlines it as four books in one. The first “book” lays out his list of Pathways of Aging, which lists what Dr. Greger thinks can be addressed with diet, including autophagy, telomeres, and inflammation. The list is appropriate, and each section includes recommendations, usually plant-food-based, on how to slow the aging of that pathway.

The second book covers anti-aging regimens. Eight of the thirteen sections deal with diet, although without the clarity of addressing a specific health metric, it rambles without clear benefits or recommendations.

The last book is Dr. Greger’s Anti-aging Eight, which is the most haphazard. It starts reasonably, echoing his previous books recommending daily consumption of nuts, greens, and berries. After those three, the book again becomes less focused, discussing new concepts (Xenohormesis! NAD+! MicroRNA Manipulation) without specific measures that could be done to access them or their health benefits. For example, the last subsection of the section is “Preserving NAD+ by tamping PARP-1 and CD38.” I read it. After reading it, I still don’t know where PARP-1 and CD38 can be found or what they do.

Some other concepts in the Anti-aging Eight are clearer, but the evidence for them is mixed. One thrust is to cut back on calories, cut back on protein, cut back on essential amino acids (which make up proteins), and cut down on methionine (another amino acid). While vermin studies (rats, mice, flies, worms, etc.) show benefits from restrictions, it is not confirmed this is true for humans. The largest human study, CALERIE, found benefits (lower blood pressure, better cholesterol levels, etc.) but also negatives (lower bone density, slower healing, increased infections). As an example of Dr. Greger’s irrational exuberance, he says that despite reducing calories by 10% in the CALERIE study, the participants got stronger over the two years. What? Chasing down the online link, I see that they lost 3% of muscle over two years. Dr. Greger calls this “getting stronger” because they lost more fat than muscle, which means lean mass body percentage increased from 70% to 72%.  “Getting stronger” is a strange description for losing 6.6 lbs. (3kg) of muscle.

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The protein restriction also has adverse effects, which Dr. Greger points out to his credit. These include increased blood pressure and increased hunger. The increased hunger is due to the “protein leverage” effect, where the body attempts to make up for the low protein content in the diet by increasing hunger. For both of these issues, Dr. Greger recommends you plant food harder, thereby reducing your blood pressure and losing weight despite increased hunger.

How Not to Age: the Unaging Assessment

But does Dr. Greger cover the basics? The book is How Not to Age, not Why I Love Plant Food, so let’s see how it fares in an Unaging Assessment.


Given Dr. Greger’s strong plant-based diet preference, it’s no surprise that his recommendations check every box for plant-based foods. Throughout the book, he recommends whole grains, legumes, fruits, and vegetables. From praising the Okinawan centenarians for eating a sweet potato-based diet to arguing that beans reduce dementia, the book is packed with recommendations on plants for any health issue. 18/18 years of longevity captured.

Despite calling out Big Tobacco and Big Pharma-funded studies as untrustworthy, he gives a pass to Big Berry-funded studies, which convince him that berries provide benefits over all other fruits. I can understand that berries are particularly yummy in a primarily plant-based diet. Still, the Hazard Ratio for berries vs. other fruits doesn’t show any particular fruit is better than the others.

Dr. Greger’s only miss on diet is his rejection of fish for longevity. In the Diet section of his Optimal Anti-Aging Regimen, fish shows positive or neutral associations with health outcomes in 98% of pooled analyses, meta-analyses, and systematic reviews. This is higher than other health-promoting food groups like legumes, whole grains, nuts and seeds, and even vegetables.

Despite the evidence supporting the benefits of fish consumption, Dr. Greger misrepresents the effects of fish by grouping fish with other animal products when discussing the adverse health effects of animal-based foods. This is misleading, as it implies that fish is detrimental to health, even when the studies he cites specifically identify fish as the healthiest source of protein for reducing premature death. Not scooping up fish costs him 1.2 years of life.


Dr. Greger’s treatment of exercise in his book is surprisingly limited despite his deep health expertise. Although he acknowledges the overwhelming evidence supporting the health benefits of physical activity, he questions whether the longevity benefits of exercise are genuine. He suggests that the correlation between lifespan and exercise is caused by good genetics, which both extend life and increase the inclination to exercise. To support this notion, he cites an identical twin study that found no statistical difference in longevity between the twins who exercised and those who didn’t.

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However, this conclusion is misguided. The study didn’t find a statistically significant difference in lifespan between exercising and non-exercising identical twins because the study was underpowered. Identical twins are rare, and identical twins where only one engages in regular vigorous exercise are even rarer — in this study, they only identified 34 such pairs. Fortunately, we can look to the same study for more compelling evidence on the relative impact of genetics versus exercise on longevity. The study also included survival rates for 134 non-identical twins and 2,100 pairs of unrelated individuals. Non-identical twins still share half of their genetic code, so if genes played a significant role in the survival of sedentary siblings, we would expect to see a lower longevity benefit for the exercising twin compared to unrelated pairs. However, the study found that the vigorously exercising sibling in a non-identical twin pair had a premature death hazard ratio of 0.72, nearly identical to the 0.73 hazard ratio for vigorously exercising individuals in unrelated pairs. As expected, capturing the longevity benefits of exercise requires exercising, not relying on favorable genetics.

Dr. Greger captures none of the possible 9.8 years for life extension from aerobic or high-intensity interval training (HIIT).

Dr. Greger at his walking desk
Dr. Greger walking more than 3,000 steps daily at his treadmill desk.

Dr. Greger’s coverage of low-intensity physical activity, such as walking, is disappointingly brief. Despite appearing in Q&A videos using a treadmill desk, similar to mine, he only briefly covers the benefits of walking in his Lifestyle chapter. He recommends walking half an hour daily, about half as much as the average American. Ironically, while Dr. Greger argues that his nutrition advice shouldn’t be watered down to what’s attainable by average Americans when it comes to walking, he doesn’t even advise them to walk as much as they already do. (-11 years)

In the first two pages of the “Preserving Your Muscles” section, Dr. Greger credits strength training with the benefit of helping to gain or regain strength, even in senior years. It’s best to focus on this point and not delve into the remaining ten pages of the chapter, which are filled with dubious diet-based approaches to preserving muscles, such as eating blueberries, garlic, spinach, fiber, or cacao. Nonetheless, Dr. Greger does acknowledge the importance of strength training in maintaining muscle mass and function throughout life. (+3.1 years)

Healthy Habits

I’m afraid Dr. Greger mostly misses on good longevity habits. Even in the food area, he is entirely silent on the benefits of spices. He doesn’t mention hot peppers, which he said in other places he loves and has proven longevity benefits. (-1.5 years) The longevity benefits of saunas or hot baths are also omitted. Perhaps he misses them because he doubts that exercise is worth it, so he never sees a gym that might have a sauna. (-5.2 years)

He warns against smoking (Am I setting the bar too low?), frequently using it as the benchmark for how unhealthy something is. “…The amount of life lost from each burger is [like] smoking two cigarettes.” (+9.7 years)

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He passes on the health benefits of glucosamine, saying the evidence for joint benefits is weak (true), and he’s not sure the longevity benefits aren’t due to the “healthy user effect.” Given that the benefits of glucosamine seem concentrated in respiratory issues, I believe this is a real opportunity that Dr. Greger misses. (-1.3 years)

In the Preserving Your Teeth chapter, Dr. Greger leaps right into his diet focus and never tells people the fundamentals—brush your teeth and visit the dentist! Maybe he thinks his readers already do this, but 12% of people report not going to the dentist yearly, and 14% don’t brush their teeth at night, the most critical time.1 He does passingly mention flossing is recommended daily and notes waxed and unwaxed floss have about the same effect. (-1.3 years)

Finally, regarding beverages, Dr. Greger gets the science right. He warns against sugary drinks, which have the most harmful effects, and while he doesn’t recommend coffee, he does say drinking tea can add two years to your lifespan. (+3.8 years)

Where the How Not To Age Shines

A third section of the book, Preserving Function, applies Dr. Greger’s encyclopedic knowledge to specific solutions to body functions and how to prevent them from aging. While you may be skeptical of a bald man with advice on “preserving your hair,” this is where you can find specific advice for most concerns about aging. Several interventions in this section had me jumping for my computer to confirm the studies backed up his claims, and generally, they did.

For bowel and bladder function, he shares several studies showing cranberries or cranberry powder improve issues. In Preserving Your Skin, he provides a good overview of sunscreens, the uselessness of collagen supplements, and diet impacts. For your sex life, he recommends fenugreek as a natural testosterone booster for both men and women.

This section is 250 pages long, and I wish the whole book had been focused on it. While I did spend some time looking up the supporting studies to see if they were significant (Rosemary oil will probably not save your hair), it was great to have an overview of the latest studies on the important functions of the body and Dr. Greger’s thorough citations allowed me to confirm the summaries.

I hope we see more like this in any future books!



  1. Dental Health Behaviors, Dentition, and Mortality in the Elderly: The Leisure World Cohort Study

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