Wednesday, May 30, 2012

Food And The Brain

This post about neuropeptides in food led me to the work of Dr. Sarah Leibowitz (photo at right). She's spent decades studying the relationship between food and the brain.

In a nutshell:
"Specific neurobiological systems and diet intake are functionally linked within a positive feedback loop, whereby a specific diet stimulates particular brain neurochemicals that in turn stimulate further consumption of that same diet. This diet-neurochemical-diet feedback process, while appropriate for producing overeating and gorging under conditions when food is scarce, helps to explain the eating and body weight disorders that develop when sugar- and fat- rich foods are abundant."
- Dr. Sarah Leibowitz, Rockefeller University Laboratory of Behavioral Neurobiology
A positive feedback loop. So... Eat sugar, crave sugar. Eat fat, crave fat (and alcohol, see below).

Some brain chemicals and their actions:

Norepinephrine - stimulates food intake, preferential to carbs, secreted at weaning and high corticosterone
Neuropeptide Y - stimulates food intake (counteracted by leptin), preferential to carbs, secreted at weaning and high corticosterone
Galanin - stimulates food intake, preferential to fat esp. saturated and to alcohol, secreted at puberty and estrogen-rich periods in a woman's cycle
Enkephalin (opioid) - stimulates food intake, preferential to fat esp. saturated and to alcohol
Dynorphin (opioid) - stimulates food intake, preferential to fat esp. saturated and to alcohol
Orexin - stimulates food intake, preferential to fat esp. saturated and to alcohol
Serotonin - reduces appetite and produces satiety
Dopamine - reduces appetite and produces satiety

Fast Response Times
"These effects of diet on the hypothalamus are found to be amazingly rapid, occurring within the context of a single day — or even a single meal."
Early Exposure to Imbalanced Diets Sets One Up For Obesity
"In a particularly exciting animal model developed and characterized in our laboratory, we have demonstrated that sugar- or fat-rich diets introduced early in life, even during pregnancy, can produce profound changes in circulating nutrients and brain neurochemical systems. These changes persist over time, even after the diet is returned to a balanced mixture, and they result from an increase in cell proliferation and neurogenesis in specific peptide systems that ultimately cause the offspring to overeat and become obese as adults."
Fat And Alcohol Linked
"There exists a positive feedback loop between these peptides [galanin, enkephalin, dynorphin, orexin] and alcohol intake, which is similar to that seen with dietary fat and may be involved in promoting the over-consumption of alcohol as well as a fat-rich diet. ... Together, this evidence suggests for the first time that alcohol and fat intake during a meal may synergize to produce larger meals and greater alcohol consumption."
So... Eat fat, crave fat and alcohol. Eat alcohol, crave fat and alcohol.

High Carbohydrate Diet May Reduce Appetite, Feeding, And Body Weight

Some of Leibowitz's newer research seems to be a leap, or maybe a fine-tuning of her earlier work. She focused on a chemical in the brain called Hypothalamic Huntingtin-associated protein 1 (Hap1). Levels of Hap1 are reduced by a high-carbohydrate diet. Lower levels of Hap1 "mediate the feeding-inhibitory action of insulin in the brain," and can result in a decrease of food intake and body weight.
Hypothalamic Huntingtin-Associated Protein 1 As A Mediator Of Feeding Behavior, Nature Medicine, April 2006

That a high-carb diet could result in weight loss reminded of this study...
A Low-Fat Vegan Diet Improves Glycemic Control and Cardiovascular Risk Factors in a Randomized Clinical Trial in Individuals With Type 2 Diabetes, Diabetes Care, 2006
...which saw people with type 2 diabetes who were eating a high-carb diet (over 70% of their calories from carbs) lose twice as much weight as people eating the lower-carb, higher-fat ADA diabetes diet. (My review: High-Carb, Low-Fat Diet For Diabetes)


Bix said...

The question comes up ... what is a high-carb diet? In studies such as this one (Diabetes Care 2006) the high carb diet included things like rice, beans, potatoes, yams or sweet potatoes, oatmeal, quinoa, squashes, carrots, apples, and other low-fat low-processed vegetables and fruits. It does not usually include things like breakfast cereals, breakfast bars, muffins, pancakes, cookies, crackers, chips, which are highly processed and often made with fat.

Bix said...

Interesting ... that link between consumption of fat, and craving and consumption of drugs ... alcohol, nicotine, maybe cocaine.

Laurie Endicott Thomas said...

High-carbohydrate simply means that a high percentage of the calories (75% or more) are from starches and sugars. Most breakfast cereals, with the exception of some granolas, are high carbohydrate.
The original diet that Dr. Walter Kempner used for his patients with kidney disease and diabetes and so on was based on rice and fruit. If the patients lost too much weight on that low-fat diet, they were encouraged to add pure sugar. About 90% of the calories in that diet were from carbohydrates.
Kempner's high-carb diet reversed type 2 diabetes and helped patients with type 1 diabetes reduce their insulin resistance and improve their overall health. The diet described in the Diabetes Care article was intended to be as high as possible in fiber because the diet was intended to promote rapid weight loss. That's why there was so much emphasis on minimally processed food.

caulfieldkid said...

That's what I've been saying for a while now. "Look, Charlie Sheen isn't a bad guy. He just needs to ease up a bit on all the fat in his diet."


Bix said...

Lol, shaun.

It's weird. As you said, it makes you wonder if cutting back on fat might help someone who is struggling with a smoking habit. Or with alcohol. Or something stronger.

Bix said...

There's a little more to it, Laurie. Carbs are not all alike. Some, like breakfast cereals, make us put weight on easier than others, like cold potatoes.

Resistant starches, which are carbs, help us lose weight.
Processed starches, which are carbs, help us gain weight.

And it's not a matter of calories. I'll see if I can find that post about processed food.

Here it is:

Ben P. DaSalt said...

One tactic I’ve noticed critics who dismiss epidemiological data of plant-based diets, in particular good results for vegetarian populations, note that they are not healthy because of vegetarianism per se, but because of other associated, though unrelated health habits, like lower rates of smoking and drinking and other health related activities that health minded people pursue.

But perhaps there is a causal relation. Perhaps lower fat plant-based diets enable healthier associated habits.

Bix said...

omg. I never thought of that, Ben.