The See Food Diet: Brain Activity and Weight Loss
There are hundreds — if not thousands — of different diets out there for people to lose weight. Yet there are more obese people now than ever before. How can that be?
Well, first, it seems that many of these diets do work. People do lose weight –- at least in the short term.
But very quickly (say, in a year) people gain back the weight and then some.
People who take part in behavioural weight-loss programs lose weight — on average 9 kg, or around 10% of their body weight, in the first 6 months of the program.
Then things start to slide.
After 1 year, they will regain a third (3 kg) of the weight loss (1). In 5 years, people are back to where they started (2). That’s not good.
But a small percentage (such as many of our PN members) keep the weight off successfully, for life. Why?
Well, the National Weight Control Registry wants to find out.
The NWCR tracks people that were successful at long-term weight loss. In order to be part of the NWCR, people need to maintain a weight loss of more than 13 kg (30 lb) for more than a year.
The NWCR has found a few interesting and promising things.
For example, successful weight loss maintainers work harder than people who were of normal weight all their lives.
What does that mean? Successful weight loss maintainers say they eat less fat, weigh themselves more and do more exercise than people with no history of obesity or weight loss.
So the good news is you can lose weight and keep it off, but the bad news is you’re going to have to put more effort in than a lifelong skinny person. (For other factors involved in successful weight loss, check out the NWCR’s site.)
But why do people have to put in more effort in the first place? Are these successful weight losers different biologically than those who gained back the weight?
This week’s review looks at a study that compares how the brain responds to food in successful weight losers, normal weight people and obese people.
McCaffery JM, et al. Differential functional magnetic resonance imaging response to food pictures in successful weight-loss maintainers relative to normal-weight and obese controls. Am J Clin Nutr. 2009 Oct;90(4):928-34. Epub 2009 Aug 12.
Methods
This study is a bit different than most of the studies I’ve reviewed.
Most studies I’ve reviewed are called intervention studies, in which the researchers intervene to see what effect the intervention has. For example, in a supplement study, the intervention is the supplement.
Most of the studies I’ve reviewed are random (randomized intervention studies) where the participants are randomly assigned into the control group (no intervention) or the experimental group (an intervention such as supplements, exercise, diet, drugs or anything else you could think of).
The study this week is an observational study, meaning the researchers just observe what’s going on without intervening then afterward they try to figure out what was correlated to what.
The advantage with these types of studies is you don’t need to worry about the participants doing what you want them to do – they just carry on with their lives.
The disadvantage is self reporting – are the participants honestly and accurately reporting their activities? Sometime people lie, but more often there is a discrepancy in perspective. They may forget about the donut they eat, or they report a small donut when in fact it was a huge donut.
The participants
For this observational study, there were three groups divided based on lifetime weight. The groups were:
- Normal weight (NW): lifetime maximum BMI of 24.9 (and minimum of 18.5)
- Obese weight: current BMI of over 30
- Successful weight-loss maintainers (SWL): previous BMI of over 30, current BMI between 18.5 and 24.9, lost over 30 lb (13.6 kg) and maintain weight loss for at least 3 years.
As you can see the last group (SWL), is a very specific group that were obese, but lost weight and have maintained a normal BMI for at least 3 years.
The groups broke down into 18 NW, 16 obese and 17 SWL participants in their mid-forties and mostly women.
Visual food cue paradigm
Visual food cue paradigm is some fancy talk for flashing pictures of different foods in front of someone’s face.
In this case, pictures flashed were either:
- low-energy foods (whole-grain cereals, salads, fresh vegetables and fruit);
- high-energy foods (cheeseburgers, hot dogs, French fries, ice cream, cake and cookies); or
- non-food (rocks, shrubs, bricks, trees, and flowers).
I’m sure the first thing you notice is the breakdown of supposed low & high energy foods. I think a better description would be healthy versus unhealthy food, as whole-grain cereal isn’t exactly low-cal.
So why flash pictures of food and non-food items?
To torture them? As a new marketing strategy? Nope.
Researchers want to see whether NW, obese, and SWL respond differently to food cues (aka pictures of food).
MRI
Using a magnetic resonance imaging (MRI) scan while the participants looked at pictures of food, the researchers could match up activity with certain areas of the brain that light up in response to food. Then they could compare to see if the groups respond differently to food cues.
Results
After splitting up the groups, flashing pictures, and taking pictures of brains, the researchers found that NW, obese and SWL responses to visual food cues were indeed different.
Comparing blood oxygen level-dependent signals (measured by MRI), four regions of the brain were found to be different between groups.
SWLs had greater activation of the left superior frontal region (left, top, front part of the brain ) and right middle temporal region (right, middle, in front of the ear part of the brain) compared to obese and NW.
Self control and food awareness
This greater activation means that the SWL group has greater inhibitory control. In order to maintain their weight loss the SWLs need to maintain control of their food intake. That requires a high level of dietary restraint (3,4).
So when the SWLs look at pics of food they have to work harder (demonstrated by more blood to specific areas of the brain) to stay in control.
People who lost weight and kept it off had greater visual attention to food. This is very helpful when you’re trying to pick out food that isn’t going to cause you to gain weight. This is what the researchers call food monitoring.
To successfully keep the weight off you need to know what foods are “good” and “bad”; avoid “bad” foods and focus on “good” foods; and keep track of what you’re eating. In other words, you need to pay attention!
Don’t eat that!
Another interesting thing, SWLs have low scores of dietary disinhibition (5).
Say what? Don’t you not like double negatives?
Translation of “SWLs have low disinhibition” is they have restraint.
Conclusion
In the end, yes there is a different in the brain response to food (pictures at least) in SWL, NW and obese. But is this a process of selection or conversion?
Selection or conversion
What do I mean by selection or conversion?
In this study researchers showed a difference in brain activity between people who successfully lost weight and keep it off compared to normal people and obese people.
But the real question is: Were the successful losers selected to have greater brain activity before they lost the weight? Did they already have the food knowledge and self control that made them successful?
Or did they put more effort into monitoring their food, an effort that led to a change in their brain — making it more active in certain regions?
In other words, which came first, the chicken of brain activity or egg of weight loss?
Bottom line
While the study clearly finds that successful weight losers have different brain activity, they don’t know if the difference is innate or a consequence of effort and habit.
Humans are, after all, quite clever creatures who are capable of learning and adapting to many things.
So give yourself the benefit of the doubt: Either believe you have the right mind to be successful or that you have the power to change your mind.
References
1) Behavioral approaches to the treatment of obesity. Wing RR. In:Bray GA, Bouchard C, James WPT, eds. Handbook of obesity. New York, NY: Marcel Dekker Inc. 1998:855-73
2) Treatment of obesity by very low calorie diet, behavior therapy, and their combination: a five-year perspective. Wadden TA, Sternberg JA, Letizia KA, Stunkard AJ, Foster GD. Int J Obes. 1989;13 Suppl 2:39-46.
3) A descriptive study of individuals successful at long-term maintenance of substantial weight loss. Klem ML, Wing RR, McGuire MT, Seagle HM, Hill JO. Am J Clin Nutr. 1997 Aug;66(2):239-46
4) Long-term weight loss maintenance. Wing RR, Phelan S. Am J Clin Nutr. 2005 Jul;82(1 Suppl):222S-225S. Review.
5) Internal disinhibition predicts weight regain following weight loss and weight loss maintenance. Niemeier HM, Phelan S, Fava JL, Wing RR. Obesity (Silver Spring). 2007 Oct;15(10):2485-94.