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Written By: Dr. Barry Sears Creator of the Zone Diet

Written by Dr. Barry Sears
on January 04, 2016

I very rarely recommend diet books because most of them are either rewrites of my basic ideas presented in The Zone (1) more than 20 years ago (i.e. excess insulin and excess inflammation make you fat, sick, and age faster) or are based on unsustainable ideas that are presented as “scientific facts” (i.e., gluten kills, saturated fats are good, etc.). Unfortunately, today everyone who eats considers himself or herself to be a dietary expert. Frankly, there are very few real diet experts. One of the few is David Ludwig at Harvard Medical School. That’s why I recommend his new book, Always Hungry? (2)

I have known David for more than 20 years. He was the first academic researcher to confirm the hormonal effects described in The Zone as well as the ability of the Zone Diet to suppress hunger. (3,4) However, those clinical trials were the result of initially intense skepticism on his part.

When The Zone first appeared in 1995, David would continually walk by the book in the local bookstore almost outraged by its garish title colors and outrageous claims (like “lose weight permanently” among others) on the front cover. After doing this same routine after another four or five visits to the bookstore, he decided to buy the book to read the pseudo-scientific hogwash inside the book. Much to his surprise, The Zone was not a diet book, but a book on diet-induced hormonal responses. Through a mutual contact, David invited me to give a seminar to the Department of Pediatric Endocrinology at Harvard Medical School. Before the seminar started, he warned me that, “these guys would likely eat their kids for lunch,” meaning that I should be prepared for scientific grilling. Although most of my lecture focused on the biochemical pathways of diet-induced inflammation, at the end I asked if there were any questions? Most of the people in the seminar thought what I had outlined was reasonable. However, there was one question from the back of the room from the department chairman. He said, “I don’t understand these eicosanoids?” I told him to simply focus on keeping insulin in a zone, and the eicosanoids would take care of themselves.

Needless to say, they were intrigued with my ideas since they were contrary to the prevailing winds blowing through Harvard at the time that low-fat, high-carbohydrate diets were God’s gift to mankind. Being always the scientist, David wrote a grant to the National Institutes of Health to do a clinical study to either prove or disprove my theories. You can image his surprise when the grant was rejected outright. So the department dipped into its slush funds to design and do its own definitive study. This was a very lucky break for me because David put together a highly controlled clinical study on hormonal responses and the effect on hunger in an inpatient metabolic ward that would never be approved by the government. (Most government-sponsored diet studies still ask only simple-minded questions on differences in weight loss by letting people eat on their own after getting some minimal dietary advice).

The first study they designed was a crossover study. This is really the platinum standard for diet studies. Since the same subject is used to test several diets, this type of clinical study rules out any possible confounding genetic differences. The three diets they decided to test were composed of the following meals: (a) a high-carbohydrate meal using instant oatmeal, (b) a high-carbohydrate meal using steel-cut oatmeal to give a lower glycemic response, and (c) a Zone Diet meal consisting of an egg white omelet and fruit (40% calories as carbohydrates, 30% calories as protein, and 30% calories as fat).

This well-designed trial would demonstrate the relative impact of the glycemic load of a meal versus the macronutrient ratio in these three isocaloric meals (all meals contained 392 calories) as well as test differences in hormonal responses and hunger in the same subjects with the same genes. The best way to test hunger control is to make sure the subjects are overweight, if not obese, and give them calorie-restricted meals (like 392 calories for each meal) to make them really hungry. The first trial they did was using obese adolescents in Boston (very easy to find for a clinical trial offering free food).

The night before the trial, each research subject was given the 392-calorie Zone meal in the metabolic ward. Then the next morning they were given one of the three different test meals so the researchers could follow the hormonal changes in their blood for the next five hours. After taking out the blood catheters needed for the blood testing, they were given exactly the same breakfast meal for lunch. During the next five hours in the afternoon, they were allowed to sit quietly eating all they wanted from a buffet consisting of platters of tasty foods like bread, bagels, cold cuts, cream cheese, regular cheese, cookies and fruits. This remains one of the best-designed trials I have ever seen in the last 20 years of diet research to look at hormonal responses and the effect of those hormonal responses on hunger. This is far too complex for a typical government grant, but if you are going to spend your own money, why not do the best possible research?

So what happened? They found some positive effects of replacing the instant oatmeal with steel-cut oatmeal (but a high-carbohydrate meal is still a high-carbohydrate meal when it comes to hormonal changes), but very dramatic hormonal changes when eating the Zone Diet meal. The insulin levels were reduced, the glucagon levels dramatically increased on the Zone Diet meal just as I had predicted they would when I wrote The Zone. Relative to hunger, for the first five hours after the test breakfast, they experienced far less subjective hunger than on the other two test meals. Then after eating the same meal for lunch as they had eaten for breakfast, they had access to the buffet in the metabolic ward during the afternoon meal. These obese children ate 150-650 fewer calories at the buffet after eating two Zone Diet meals compared to the times they ate either of two high-carbohydrate non-Zone meals. In this phase of the study, the steel-cut oatmeal-based meal appeared to be more satiating than the instant oatmeal-based meal. So let’s use 400 calories less per meal as an average calorie difference between eating two Zone meals versus two high-carbohydrate meals. If you eat 400 fewer calories per day for month, you should lose about three pounds of fat per month.

Just to be sure, David did another crossover experiment with overweight and obese adults (also easy to find in Boston). In this study they only compared two calorie-restricted diets: a high carbohydrate diet and the Zone Diet (43% calories as carbohydrates, 27% calories as protein, and 30% calories as fat). Both diets were relatively high in fiber (about 27 grams per day). For six days they ate only 1,642 calories per day consisting of three equal-sized meals and a bedtime snack (as I described in The Zone). Then, on the next two days (days 7 and 8) they ate the same 1,632 calories, but now they could eat as many additional calories as they wanted from a cold-cut buffet in the metabolic center. When they ate the high-carbohydrate, low-fat diet for 8 days, they consumed an additional 836 calories over the two extra food access days compared to when they consumed the Zone Diet for 8 days. This would suggest if you eat a Zone Diet, you would consume about 400 less calories per day because you were simply not as hungry. I guess I was right about dramatic hormonal changes and less hunger a person would experience following the Zone Diet.

In my opinion, these two clinical trials conducted by David remain the best-designed trials ever published to study the relationships of hormonal responses and hunger. I guess this is what happens when you fund your own research and not beg for a government handout.

Now let’s fast-forward to 2016 to David’s new book, Always Hungry? The basic hypothesis in this book is similar to the one that I subscribe to and wrote about in my book, Toxic Fat, published in 2008. The common hypothesis is that obesity is the consequence of incoming calories being trapped in our fat cells thus causing the rest of the body to starve. When you are starving, what do you do? You either eat more calories or slow down physical activity. In other words, you become a glutton or sloth. Usually both happen simultaneously. Once you have developed a Fat Trap, trying to eat less or exercise more only compounds the basic problem that leads to obesity: increased hunger.

I consider David to be one of the leading nutritional scientists of the 21st century as well as being an extremely fastidious clinical researcher. That’s why I highly recommend his book. Do we have some differences? Of course we do, but they are relatively minor in terms of our shared views on the underlying cause of obesity.New call-to-action


  1. Sears B. The Zone. Regan Books. New York, NY (1995).
  2. Ludwig D. Always Hunger? Grand Central Life and Style. New York, NY (2016).
  3. Ludwig DS, Majzoub JA, Al-Zahrani A, Dallal GE, Blanco I, and Roberts SB. “High glycemic index foods, overeating, and obesity.” Pediatrics 103:E26 (1999).
  4. Agus MS, Swain JF, Larson CL, Eckert EA, and Ludwig DS. “Dietary composition and physiologic adaptations to energy restriction.” Am J Clin Nutr 71:901-907 (2000).
  5. Sears B. Toxic Fat. Thomas Nelson. Nashville, TN (2008).

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