Those who are obese have a greater desire for, and more difficulty resisting sweet high calorie foods than a lean person when blood sugar drops, even just a little. And when cortisol kicks in the effect is enhanced.
As someone who suffers reactive hypoglycemia, I know it is virtually impossible to resist any kind of food when your brain is literally starving. Eating a paleo / ‘zone-ish’ diet* has given me freedom from the dreaded blood sugar crashes, and consequent overeating.
(*By Zone-ish I mean sticking to the principal of protein and some fat with low to moderate carbs at each meal)
ScienceDaily (Sep. 19, 2011) — If the brain goes hungry, Twinkies look a lot better, a study led by researchers at Yale University and the University of Southern California has found.
Brain imaging scans show that when glucose levels drop, an area of the brain known to regulate emotions and impulses loses the ability to dampen desire for high-calorie food, according to the study published online September 19 in The Journal of Clinical Investigation.
“Our prefrontal cortex is a sucker for glucose,” said Rajita Sinha, the Foundations Fund Professor of Psychiatry, and professor in the Department of Neurobiology and the Yale Child Study Center, one of the senior authors of the research.
The Yale team manipulated glucose levels intravenously and monitored changes in blood sugar levels while subjects were shown pictures of high-calorie food, low-calorie food and non-food as they underwent fMRI scans.
When glucose levels drop, an area of the brain called the hypothalamus senses the change. Other regions called the insula and striatum associated with reward are activated, inducing a desire to eat, the study found. The most pronounced reaction to reduced glucose levels was seen in the prefrontal cortex. When glucose is lowered, the prefrontal cortex seemed to lose its ability to put the brakes upon increasingly urgent signals to eat generated in the striatum. This weakened response was particularly striking in the obese when shown high-calorie foods.
“This response was quite specific and more dramatic in the presence of high-calorie foods,” Sinha said.
(And the reality is – we are always surrounded by ‘delicious’ high calorie, tempting foods, unless we are in a metabolic ward in a hospital experiment)
“Our results suggest that obese individuals may have a limited ability to inhibit the impulsive drive to eat, especially when glucose levels drop below normal,” commented Kathleen Page, assistant professor of medicine at the University of Southern California and one of the lead authors of the paper.
Brain reward regions are activated when glucose levels drop below normal, (blue). In lean people, but not in the obese, the prefrontal cortex which is involved in decision making and regulating impulses are activated when glucose levels return to normal, (red). (Source: journal article)
A similarly robust response to high-calorie food was also seen in the striatum, which became hyperactive when glucose was reduced. However, the levels of the stress hormone cortisol seemed to play a more significant role than glucose in activating the brain’s reward centers, note the researchers. Sinha suggests that the stress associated with glucose drops may play a key role in activating the striatum.
And from the original study report:
A number of peripheral hormones involved in feeding behavior, including leptin, peptide YY, and insulin, act as satiety signals and have been shown to deactivate homeostatic and hedonic brain regions (23–26). In contrast, the gut-derived orexigenic hormone ghrelin activates motivation and reward regions, including the insula and striatum, in response to food stimuli (27). In the current study we observed that mild glucose reductions engage these brain motivational centers to increase hunger and food-seeking behavior. This effect was seen in the absence of changes in circulating insulin, leptin, or ghrelin but was associated with higher levels of cortisol, which was positively correlated with activation of the insula and striatum. Behavioral studies in humans have shown that stress-induced elevations in cortisol secretion increase preference for calorie-dense foods (28), and our findings may provide a neural basis for this response….
We conclude that the glycemic state modulates the complex interplay between the PFC and hypothalamic and mesolimbic neural control of food-seeking behavior. Transient modest reductions in circulating glucose decrease prefrontal cortical inhibitory control and could promote overeating, particularly in an environment inundated with visual cues of high-calorie foods. These data imply that strategies to minimize postprandial decrements in glucose, including consumption of smaller, more frequent meals, may be helpful in reducing the risk of overeating high-calorie foods, particularly in obese individuals.
“The key seems to be eating healthy foods that maintain glucose levels,” Sinha said. “The brain needs its food.”
Kathleen A. Page, Dongju Seo, Renata Belfort-DeAguiar, Cheryl Lacadie, James Dzuira, Sarita Naik, Suma Amarnath, R. Todd Constable, Robert S. Sherwin, Rajita Sinha. Circulating glucose levels modulate neural control of desire for high-calorie foods in humans. Journal of Clinical Investigation, 2011; DOI: 10.1172/JCI57873
Hypoglycemia, or more accurately, reactive hypoglycemia is usually set in motion by eating foods that raise the blood sugar high very quickly. It doesn’t necessarily mean eating a lot of carbohydrates, mine will rise with just a small handful of dried fruit or 1/2 cup of rice (about 20 grams of carbs) if eaten on its own. Those with a trigger happy insulin response i.e. a high insulin secreter will tend to send out a lot of insulin. Before a person becomes insulin resistant, they may in fact be very insulin sensitive. The insulin ‘docks’ in to the receptors on cell membranes, effectively telling the cell to allow glucose to flow from blood stream in to cell, in order to lower blood sugar to a more desirable level. If too much is removed, blood sugar drops too low and hypoglycemia ensues.
When I get hypoglycemic, I get dizzy, and I can’t see straight – almost as though I’m going to black out, I get shaky, extremely irritable and cannot think of anything but getting something to eat to get my blood sugar back up. Sugar really is the only thing the brain is after and it is easy gorge on something sweet and go through the cycle again.
In a previous post, I posted a graph which showed the blood sugar response to 3 different meals, instant oats, slow cooked oats and vegetable omelet and fruit.
The stress hormone increase shown in the graph above is in response to the blood sugar dipping so low. While insulin is still high, and glucagon suppressed (no protein in the meal) glucose cannot be released from storage, so epinephrine is released from the adrenal glands, which triggers glycogen release from the liver, converts it to glucose and so raises blood sugar. Epinephrine leaves one feeling jittery, sweaty and shaky.
Blood sugar control – particularly guarding against low blood sugar drops – is therefore imperative to gain control of our desires for high calorie sweet foods. The only way I know how to do this is to eat meals that contain a moderate amount of protein, a little carbohydrate and a decent amount of fat. The carbohydrate amount depends on each person. I personally find a little is good, but none leaves me searching for more food. Increasing blood sugar and insulin a little helps with satiety in my experience. Experiment and find a balance that works for you.
Decreasing stress and maintaining lower cortisol levels should help too. Lack of sleep has already been shown to increase cortisol and cause people to eat more. “Moderate sleep and less stress may help weight loss”
Take a look at this video from Dr. Eenfeldt, on high fat, high protein, low carb diets and his use of it to help his patients control blood sugar, treat diabetes and lose weight. Particularly interesting are the two graphs he shows mapping his blood sugar (starting and 27:50) after a low carb meal compared to a high carb meal.
More interesting reading: