Can We Say What Diet Is "Best"?

One recent study demonstrated that the Mediterranean diet is better than a low-fat diet at improving a wide array of cardiac risk factors. Another showed that the Portfolio Diet is superior to a low-fat diet at lowering serum lipids. But then again, very low-fat, plant-based diets have been shown to cause regression of atherosclerotic plaque, to prevent cardiac events and to modify gene expression in a manner that should lower cancer risk.

So, do we know what diet is "best"?

No, we do not. And anyone who claims we know decisively what specific diet is best for health is either misguided, selling something or both.

But what in my opinion we do know decisively is the basic theme of "best" eating -- for our health and the health of the planet. And we know a number of variations on that theme as well, opening up opportunities for the indulgence of personal preference -- or in other words, for loving food that loves us back.

For those inclined to eat only plants, a consistent body of evidence supports health benefits of a vegetarian or vegan diet. Eating only plant foods does not guarantee a healthful, balanced diet. Sugar -- among the more reviled of modern dietary excesses -- comes from plants, after all. So the potential health benefits of veganism require that it be well practiced. I recommend the work of Davis and Melina to those who need help getting there from here. A vegan diet, when well-devised, offers benefits to one's personal health and the health of the planet. Judicious supplementation will be required; intake of Vitamin B12 will be negligible, and Vitamin D levels will depend either on supplementation or routine sun exposure.

What may surprise the staunchest proponents of a vegan diet -- such as Dr. T. Colin Campbell and his many followers -- is the lack of evidence that veganism is better for our health than well-practiced omnivorousness. There are three important considerations related to this point.

First, it stands to reason that human physiology is well-adapted to certain animal foods. While paleoanthropologists may continue to debate the exact degree to which our Stone Age ancestors were gatherers versus hunters, there is consensus they were both. Animal foods -- meat, fish, eggs -- are a native part of the human diet.

Second, dietary details matter in both the animal and plant kingdoms. The category of animal foods is home to everything from wild salmon, to a wide array of salamis. Some choices are likely to promote health, others to threaten it. A one-size-fits-all assessment of the health effects of eating "animal foods" is almost certain to be erroneous.

And third, what we have here is an absence of evidence, rather than evidence of present or absent health effects. Consider the study it would require to prove that a vegan diet, or optimized omnivorous diet, were superior to the other: thousands of people, randomized to one of several dietary patterns, and then followed for decades. Even if there were people willing to enroll in such a trial (doubtful!), costs would be prohibitive. For now, we may simply acknowledge that no such trial has been conducted.

So we are left with evidence of clear health benefits from some mixed diets, without any means to compare them directly to the benefits attached to plant-only diets. The Mediterranean diet -- more a class of diets than one per se -- stands out. Studies suggest benefits across a spectrum of health outcomes, from weight to cancer, cardiovascular disease to life expectancy. The benefits are not discernibly less, and could even be greater, than those chronicled for vegetarianism.

A balanced, mixed diet of plant and animal foods was used in the Diabetes Prevention Program, and produced a 58 percent reduction in the incidence of Type 2 diabetes in high-risk adults. In the various DASH diet studies, a diet including low- and non-fat dairy was more effective than a plant-based diet without dairy, at lowering blood pressure.

That said, the widespread support for the DASH diet may owe much to the rich getting richer. The DASH trials were supported by the National Heart, Lung and Blood Institute, and therefore the promising outcomes of these studies have the might of the NIH behind them. There are legitimate concerns about potential adverse effects of dairy intake that DASH-related literature tends to ignore. Nor do we have head-to-head comparisons of a DASH-style diet to a vegan diet, or Mediterranean diet, to show which produces the best long-term health effects. DASH is a good diet, to be sure -- and clearly far better than the typical American diet. But contentions that it is the "best" diet derive from good PR, not good data.

The Portfolio Diet, devised by my friend and colleague Dr. David Jenkins at the University of Toronto, was not originally intended to be a serious contender for best diet laurels. Dr. Jenkins and his team designed and tested this diet to make a point: food is powerful medicine. Specifically, they wanted to show that a well-chosen "portfolio" of foods for lipid-lowering could do the job as well as statin drugs. With a diet incorporating a hefty dose of soluble fiber and plant sterols, they showed exactly that.

But Dr. Jenkins is quick to note that 75g of soluble fiber per day is apt to be unpalatable for most people, so the Portfolio Diet was more about proof of principle, rather than guide to practice. But gentler variations on the theme of "Portfolio" eating, and the new study showing its ostensible superiority to a low-fat diet, have it in the mix.

Other work by Dr. Jenkins' team does a nice job of backing the "low-carb" diets into the appropriate corner. In general, such diets are not admissible participants in the best-diet pageant.

A truly low-carb diet is low in vegetables, fruits, whole grains, and to a lesser extent, beans and legumes as well. Proponents are quick to protest that their low-carb diet does not limit vegetables, or beans. Well then, it's not a low-carb diet, but a selective-carb diet. And every "good" diet, every reasonable contender for best-diet laurels, is already a selective-carb diet, while also preserving the good sense to include fruits. So again, truly low-carb diets are not a consideration.

But one variation on the theme of low-carb eating is a mostly plant-based diet, relatively high in protein. Dr. Jenkins and his team termed this the "Eco-Atkins" diet, highlighting a way to eat more protein without imposing the environmental harms attached to eating more meat. Perhaps Eco-Atkins deserves a spot in the diet pageant, but frankly, that's debatable. There is research to show that given a choice between achieving a low dietary glycemic load by eating less carbohydrate, or by eating better carbohydrates, eating better carbohydrate is better.

I hasten to note, since low-carb advocates will bring it up if I don't, that low-carb diets perform at least as well, and sometimes better, than the competition for weight loss over the short term. While this tends to be veiled in mystique, propagated by the likes of Gary Taubes, implying that the sources of calories matter, while calories do not. I believe that the truth is far simpler and far more compatible with the laws of thermodynamics. Carbohydrate is the largest nutrient class, and greatest source of calories, for all omnivores and herbivores alike. When omnivores "cut carbs," they tend to cut calories -- a lot. I have closely examined the calorie intake levels in some of the studies pitting the Atkins' diet against others and Atkins' was the most calorie-restricted.

More germane to today's topic, however, are the many potential, adverse health effects of an animal-food-based, low-carb diet, and the lack of any evidence linking such a diet to health benefits over time.

We might do well to consider sustainability as a feature of any diet competing to be "best." Not to put too fine a point on it, but in our voracious multitudes -- now roughly 7 billion of us -- we can quite literally destroy the planet by the injudicious indulgence of our appetites -- in particular by placing an emphasis on meat. We are fast becoming to the whole planet what locusts are to a field of wheat. And as ostensibly sentient creatures with options, we should find that had to justify.

There is an ethical case against eating animals as well; one I hear about routinely from a friend and colleague who heads up an animal ethics group at Yale. But the arguments in that area are more subtle than first meets the eye and warrant dedicated attention -- so I will return to that theme in my next post and just leave it dangling for the moment.

Limiting our focus to the direct effects of diet on our own health, we have a strong case for eating mostly plants. Adding in some concern for the fate of the planet, the case only strengthens.

The theme of healthful eating consistently emphasizes the same foods: vegetables, fruits, beans, legumes, nuts, seeds and whole grains. Some variations include fish and seafood, others do not. Some include low- and non-fat dairy, others do not. Some include lean meats, others do not. All banish highly processed foods delivering concentrated doses of refined starch, sugar, trans fat, certain saturated fats and/or salt to the realm of rare indulgence.

The contest to determine "the best" diet has simply not been run, possibly can't be and probably never will be. The theme of healthful eating, however, is very well established. Adopt your preferred variation on that theme, but stick to the theme and let the food you love ... love you back.

-fin

Dr. David L. Katz; www.davidkatzmd.com
www.turnthetidefoundation.org

 

Follow David Katz, M.D. on Twitter: www.twitter.com/DrDavidKatz

Comments

[Italian-in-NY]

11:02 PM on 11/04/2011

Low-carb diets based on animal fats are by far the best.
Science is piling up and, unlike the lipid hypothesis, is unconfutable.
To keep denying it just to promote a the grain-industry in the US is just funny.
We don't have evidence of long-term effects of low-carb diets? That's not true, they have been around for 40 years, but I'll give the author a free pass. There's evidence of long-term effects of low-fat diets though: 35% of Americans are obese and prone to diabetes.

[akerchen]

05:35 PM on 10/26/2011

Thanks to researchers like Loren Cordain, Ph.D., of Colorado State University and author of the book The Paleo Diet, and now Robb Wolf, we have come to understand that our bodies have not kept up with modern diets, and we are getting fatter, weaker and sicker as a result: http://naturalvitalitysports.com/2011/08/personal-trainer-and-best-selling-author-tells-athletes-how-to-eat-right/

[downstreamvegan]

05:37 PM on 10/02/2011

Wrong. We absolutely can identify which diet is best for humans. A vegan diet is best. And yes, vegans are selling something! We are selling an end to animal abuse and oppression. We are selling an end to the destruction of the ocean caused by industrial fishing. We are selling an end to the football fields of animals defecation that poison our air supply and pollute our water. We are selling an end to the overwhelming burden that meat eaters put on our health care system because they eat foods that make them sick and fat. We are selling an end to world hunger by using land, grain and water to grow foods that can be fed directly to the poor rather then to farmed animals. Humans are a species of animal. Since when is it impossible to identify the ideal diet for a species of animal? There is absolutely an ideal diet for human animals and a quick glance at America's health crisis tells you that animal products ain't' it.

[Italian-in-NY]

11:03 PM on 11/04/2011

Vegetables make people sicker and fatter than meat. Educate yourself before writing nonsense.

[Pennsanic]

07:02 AM on 11/05/2011

You make the most asinine posts on the subject of health and diet of anyone here. Vegetables make people sicker and fatter than meat? And, what, blueberries are worse for you than Cheetos? Get a grip.

[William Anderson LMHC]

08:45 PM on 09/28/2011

Another great article, reaffirming science and reason.

Some news: You will be interested in learning that I am collaborating on an obesity treatment program for kids with Dr. Robert Pretlow, who I think you know. You should hear about it soon. Also, I have created and launched a new website and blog with Q&As regarding weight loss. (The main reason I have been absent from the Huffpost activity) Here was one of the first questions I got: "Can dieting "ruin" my metabolism?" http://theandersonmethod.com/can-dieting-ruin-my-metabolism/

Best wishes,

William Anderson, LMHC
Author of 'The Anderson Method - Secrets of Permanent Weight Loss'
www.TheAndersonMethod.com

[Blue Longhorn]

02:21 PM on 09/17/2011

The "best" diet is individual - whatever an individual likes and can stick with long enough to reach their goals and maintain them.

Having tried almost everything listed above for almost 50 years, I opted for WLS, gastric sleeve to be exact. I'm now a total carnivore, very few carbs of any kind, if any on a daily basis. I supplement with vitamins and am happy, healthy and, more importantly have reached a goal and maintained it.

Sometimes I think there is no "best" diet.

[John Di Saia]

03:11 PM on 09/16/2011

Due to the variability between different people there is probably no one "best" diet for all people. I think generalizations are more appropriate in this light. Then again generalizations don't make anyone any money:

(1) Less or no fast food...not an advertiser favorite by any means.
(2) Less fat...to some extent supported by number (1)

[derekhenry]

03:32 PM on 09/18/2011

Only fat that should be avoided is trans fat.

[John Di Saia]

04:22 PM on 09/18/2011

Saturated fat too.

[Sarah H M Ajz]

08:34 AM on 09/11/2011

Finally an article that is scientific, and not biased in favour of cause-headed fanatics. Thank you, sir. It's all about Home-Cooked Food. Eat natural. Eat balanced. That's all I know. And that's all that works.

[tomteboda]

01:59 AM on 09/10/2011

I have observed that most people I've seen on the Atkins diet eat quite a bit more mindfully than they did before they began the diet, and eating mindfully they also eat less. Simply on observation the two things I would point to for causing weight loss in those successful are the elimination of sugary drinks and the elimination of so-called "junk food" (energy-dense, easily consumable, and tasty foods --not to imply other foods aren't tasty, just that these foods tend to be unusually so) from the diet.

It is amazing how many calories people can consume without being aware of what they're eating. I had a cousin who drank two twelve-packs of mountain dew and five gallons of milk a week. When she cut down to 3 daily 8 oz. servings of milk and eliminated the sugared pop she lost 50 lbs in six months. I'm not saying its a panacea for weightloss, but I believe what most of these diets do that makes them succeed (at all, for any period of time) is force people to think before they eat, and thus eat less.

[tomteboda]

01:59 AM on 09/10/2011

Thank you for another positive article, Dr. Katz. As a chemist (and one with a lot of background in metabolic systems), I agree with your assessment of thermodynamics and caloric intake. Our enzymatic pathways tend to work quite consistently to break down all food and convert it into simple sugars and then use the simple sugars (specifically primarily glucose, but a backup of anaerobic metabolism of lactose) to fuel our cells. While some foods break down quite rapidly and others take a few more steps, and some get shunted into storage easier than others, the ultimate destination remains the same.

[TomP100]

11:27 PM on 09/09/2011

Thank you, Dr. Katz for provided a dose of cmmon sense and sanity on a board where certain dietary groups with an agenda are given to much sway.

[Irene Rubaum-Keller]

02:19 PM on 09/09/2011

Great blog Dr. Katz. Here is my very simplified take on the diet dilemma. http://www.huffingtonpost.com/irene-rubaumkeller-/what-is-the-best-diet-for_b_105383.html. As you say, it's not one size fits all.

[Josephius]

01:45 PM on 09/08/2011

A great, well-written article!

[LovingFit]

08:13 AM on 09/08/2011

I think the best diet for anyone is the one that fits your lifestyle. There is no need to go extreme on anything, as long as the nutrition plan makes sense to you. I've tried so many crazy things in my life, just to come to a conclusion:

The best nutrition is the one that comes in the most natural form - no processed foods or sugar, lot's of water and plenty of veggies and fruits.

http://www.lovingfit.com

[hartsmart]

05:25 AM on 09/08/2011

Healthful eating very well established? Not according to my obesity recovery disclosure. Few items will pass the test.
My ideas--- New York Times-- What should Obama say? Comments--- go to # 192.

+ 1-- diets don't work.

[MaxineFox]

09:45 PM on 09/07/2011

Good article.

Regarding the Mediterranean diet... while it is a reasonable diet, there are some serious kinks in my opinion - especially regarding the use of olive oil. Most people on this diet do all or most of their cooking with olive oil and this leads to the formation of trans fat, even at low temperatures. I wrote about this recently:

http://reverse-diabetes-naturally.blogspot.com/2011/09/if-your-oil-is-smoking-youre-creating.html

Olive oil does not have enough saturated fat! Studies have shown that consuming monounsaturated oil without enough saturated fats can lead to health issues. I discuss this here:

http://reverse-diabetes-naturally.blogspot.com/2011/08/what-is-canola-oil-and-should-diabetics.html

I plan to write why coconut oil is so healthy soon.

Regarding the fiber issue... I recently discovered how much fiber figs have - more than ANY other veggie or fruit including plums/prunes - plus, they lower blood sugar (the leaves do even more so) and they're high in minerals/vitamins. They're in season now so you can get fresh ones - I've been eating them with breakfast, throwing them in salads, lightly sauteing them as a topping for chicken/fish/shrimp, and I've even come up with a fig salad dressing - they are quite versatile and delicious. Here's why diabetics should eat more figs:

http://reverse-diabetes-naturally.blogspot.com/2011/08/diabetes-and-figs-enjoy-them-while.html

[Jennifer Bertan Muroff]

06:25 AM on 09/08/2011

I find that eating less processed food in general helps with weight loss. I start every day with a nutrient dense/high fiber breakfast that is filling. I usually have Greek yogurt with with berries, almonds and fitflax http://www.fitflax.com FitFlax is a golden roasted flax and chia blend this is loaded with Omega 3's antioxidants and fiber. It is low cal/low carb and helps with weight loss.

I also have green tea sweetened with stevia.