No bread, no potatoes. Reduce rice, corn, and pasta. Beans are the perfect food.
We have been asking whether the proposition “Every event has its cause” really leads to determinism and thus pragmatically conflicts with the ordinary human presumption of free will. Thus far, 4 proposed answers – calling it a paradox, appealing to levels in the hierarchy of matter, chaos theory, and true randomness – have been found wanting. The last 3 answers addressed old and new scientific principles which don’t fully answer questions of will.
Let’s not make the mistake, however, of excluding science from the understanding of how we choose.
My medical practice in disorders of cholesterol and other fats, or lipids, often raises questions about the role of willpower. More than half of my patients would do well to lose weight in order to improve the lipoprotein profile and blood glucose readings.
The highlighted text at right shows the surprising appearance of the term “free will” in a prestigious basic biological journal, taken from an article in Cell written by Jeffrey Flier and Bruce Spiegelman, paragons in the field of metabolic biochemistry and molecular physiology. I have never seen a reference to free will otherwise outside of philosophical writing. Here free will and physiology are described as working together to influence feeding behavior.
In fighting obesity in my patients over the past 20 years, emphasis has shifted from recommending a low fat diet to recommending most commonly a low glycemic diet – that is, a diet low in starchy foods, except that beans are allowed and encouraged.
“No bread, no potatoes” has become our mantra. Reduce rice, corn, and pasta. Because of glycemic index and load, even whole wheat bread should be avoided, but sweet potatoes are okay. Beans are perfect with minimal fat, a reasonable amount of protein, and plenty of viscous fiber that greatly slows the absorption of glucose derived from starchy carbohydrate in the beans. Beans even provide a built-in warning system with bloating and gas when you eat too much.
Two leading nutrition researchers, George Bray and Frank Sacks, led a large weight loss study comparing 3 diets that varied markedly in the share of daily calories coming from carbohydrate versus fat versus protein. Calorie distribution made no significant different for weight loss. However, a small detail appeared in the Methods section of the paper. Each of the 3 diets was designed to be low glycemic. That means each diet was designed to raise the subject’s blood glucose (sugar) level minimally, including the diet high in overall carbohydrate calories – beans!
We changed our counseling advice from traditional low-fat/reduce portion size recommendations to low glycemic recommendations in 2001. The result is illustrated in the figure below, based on an analysis led by Westly Bailey, an awesome medical student working with me:
Among groups of people (N per year) with high triglyceride (blood fat) levels who needed to lose weight, weight change beyond the first year of clinic follow-up averaged +0.2% with traditional diet counseling (1998-2000), but dropped to -3.0% with low glycemic counseling. Although 3.0% weight loss on average may not seem so exciting, weight loss sufficient to provide major health benefits occurred in about 1 out of 4 patients. We continue to see similar results today.
What does this have to do with will or willpower? Hint: Glucose is the fuel that brain uses to enable thinking.
I begin to explain the low glycemic approach to patients by saying something like this:
“Your will is the decision you make whenever during the week you feel most relaxed and able to think clearly – maybe on Sunday afternoon. Take some time then to think about what and how much you want to eat during the week. Once you decide, then willpower is whether you are able to carry out the decision that you yourself have made.”
Then I add,
“I happen to believe in the will and the soul, but willpower is different. Willpower is about how this computer works [pointing to my head]. Right?”
The patient generally agrees. Willpower is about how the brain works.
Nobody has studied willpower better than social psychologist Roy Baumeister. He and science writer John Tierney published in 2011 a terrific book for lay readers entitled Willpower: Rediscovering the Greatest Human Strength. I learned a lot from the book and recommend it highly. Chapter 2 describes the powerful effect of food on willpower. Specifically this effect comes from glucose, derived from dietary sugar and starch.
What is so special about glucose? Most people know that glucose is one of 2 major fuel molecules in the body; the other is fatty acids derived from triglyceride and other fatty molecules ingested in the diet and stored in fat cells. Many are not aware that fatty acids are the preferred fuel for heart, muscle, and almost all other body tissues.
The brain is different. Fatty acid molecules can insert themselves into cell membranes and change membrane properties. Brain cell membranes must stay precisely tuned to enable the wonders of conscious thought; they cannot be subject to highly variable fatty acid levels. Fortunately fatty acids are almost entirely attached to blood proteins, and blood proteins are almost entirely kept away from brain cells by a special brain blood vessel adaptation called the blood-brain barrier. I sometimes tell patients,
“If we didn’t keep fatty acids away from our brain cells, we would think like worms instead of mammals.”
Because the blood-brain barrier blocks transfer of fatty acids to brain cells, our brains depend entirely on glucose for fuel. Now let’s look at the fuel supply for the brain with a diet high in starchy foods.
The graph shows average blood glucose readings for 8 healthy research volunteers on a scale from 70 mg/dl to 120 mg/dl through the course of a 24-hour day, beginning just after 7:00 a.m. Four spikes in blood glucose reaching 106 to 111 mg/dl occur with 3 high starch meals and an evening snack.
Ask a computer engineer if she would ever want a computer to run with an energy supply as variable as the graph shows. What’s more, the brain is responsible for securing and maintaining its own energy supply – that is, the brain must perform all the functions of computer, user of the computer, and engineer who maintains the computer. It seems possible that alarm signals may prompt subconscious processes whenever the glucose level drops precipitously. This is illustrated by the red arrows in the graph below.
Baumeister and Tierney in their book on willpower show that decision-making capacity in humans drops to a low ebb in the late evening and nighttime hours as glucose levels are falling. Is it better, then, to keep munching cookies late into the night? Momentary impulses whisper “Grab a few!” over and over. But acceding to those impulses is just another example of weak decision-making, also known as diminished willpower.
We continue to get better results in weight loss counseling today than we did before 2001. I think this is due to high glycemic foods causing willpower to drain away faster through the day and into the evening. Low glycemic foods deliver a steadier energy supply to the brain, and as a result the brain works better especially into the evening.
The weight loss results that we’re getting cannot be denied. We are tracking weight change in the patients that we see in clinic. But is it really due to a steadier energy supply to the brain? Or does it come more from our enthusiasm about a novel, fun, and exciting hypothesis? At this point rigorous scientific investigation has not yet been done. In the meantime, patients are getting benefit from lower weight.
I’ve gone through this story in considerable detail to show how scientific reasoning can apply to willpower, which we may place, in the words of Flier and Spiegelman depicted above, “at the interface between physiology and free will.”
It’s not that hard to understand. Your will is about whether you want to make an effort to eat less, so that you can enjoy better health for years to come. It’s about goals for the week that you choose on Sunday afternoon. Willpower is about whether you can meet the goals that you yourself have chosen. Maintaining a stable energy supply for your brain by eating low glycemic foods may enhance willpower. That’s a testable hypothesis for future research.
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 POUNDS LOST trial. Sacks FM, Bray GA, et al. Comparison of weight-loss diet with different compositions of fat, protein, and carbohydrate. New England Journal of Medicine 2009;360:859-73.
 Baumeister RF, Tierney J. Willpower. Penguin, New York, 2011.
 If you starve for a day, then the supply of glucose can run low and your liver will begin to make hydrobutyrate and acetoacetate, the so-called “ketone bodies,” from fatty acids to serve as an alternative to glucose as fuel for the brain. A diet extremely low in carbohydrate, like the Atkins diet, can also promote “ketosis.” Nevertheless, with a reasonably normal diet on a day-to-day basis, glucose is the only fuel the brain uses.