How to make an 'obese brain': just add saturated fat
Written by Robyn Chuter
Created Monday, 08 April 2013
The latest diet craze, the Paleo Diet, urges its followers to load up on saturated fat, found in animal flesh, eggs and full-fat dairy products, and a handful of plant products such as coconut oil. Paleo writers extol the virtues of saturated fat, claiming that its consumption is absolutely necessary for good health and weight loss.
But if you’re tempted to jump on the Paleo diet bandwagon, think twice: all that saturated fat can cause a phenomenon dubbed ‘the obese brain’, destroying your ability to regulate the amount you eat, and sabotaging your weight loss goals.
First, a little background on 2 aspects of the anatomy of your brain:
1) The blood-brain barrier. The blood-brain barrier is comprised of specially modified blood vessel cells that act like a filter, keeping potentially harmful substances circulating in the blood away from brain cells, while facilitating the passage of glucose, hormones, oxygen and other substances vital to the brain’s function.
2) The hippocampus. This seahorse-shaped part of the brain is crucially involved in memory and learning, and also in our response to stress. It forms a component of the limbic system, the brain’s emotion centre.
Now for the really scary part: Recently-published research (1) on the impact of saturated fat consumption on the brain indicates that this type of fat damages the blood-brain barrier, allowing toxins into the brain which impair the function of the hippocampus. The result of this damage is impaired learning and memory – and a vicious circle of overeating and weight gain.The research was conducted on rats, whose blood-brain barrier and hippocampal function is essentially the same ways as humans’. The rats were initially fed on standard low-fat ‘lab chow’, while receiving training in several learning and memory tasks, some of which involved the hippocampus. After the training phase, the rats were divided into 2 groups. One group was fed low-fat lab chow ad libitum (i.e. as much as they wanted), while the other group was offered food high in saturated fat, again ad libitum.Some of the rats in the high saturated fat-fed group became obese while some did not; lead researcher, Terry Davidson, points out that just like humans, some rats have a preference for high-fat food and will gorge on it when it’s offered to them, while other rats (and humans) don’t.When the researchers presented the rats with the learning and memory problems again, they found that the rats who became obese on the high saturated fat diet, performed much more poorly than the non-obese rats did on the hippocampal-dependent learning problem. Their performance on the learning task that did not involve the hippocampus was unaffected.This decline in memory and learning ability was attributed to damage inflicted on the hippocampus by impaired blood-brain barrier function in the rats who had become obese on the high saturated fat diet. Davidson commented, "We have compelling evidence that overconsumption of a high fat diet damages or alters the blood-brain barrier. Now we are interested in the fact that substances that are not supposed to get to the brain are getting to it because of this breakdown. You start throwing things into the brain that don't belong there, and it makes sense that brain function would be affected" (2).
What this means for overweight humans
In a nutshell, what the research indicates is that diets high in saturated fat are not only obesigenic (obesity-causing) in susceptible individuals; they also cause changes to the brains of obese people that in turn may fuel overconsumption of high-fat foods, making weight loss nigh on impossible. Lead researcher Terry Davidson, who is the director of American University's Center for Behavioral Neuroscience, summarises the implications of his study for humans: "What I think is happening is a vicious cycle of obesity and cognitive decline… you eat the high fat/high calorie diet and it causes you to overeat because this inhibitory system [i.e. the ability to inhibit overeating by recognising when you’ve had enough] is progressively getting fouled up. And unfortunately, this inhibitory system is also for remembering things and suppressing other kinds of thought interference [i.e. thoughts of high-calorie food that pop unbidden into your mind – generally as soon as you commit to your new weight-loss plan!]." There is strong evidence that the results of this animal study probably do apply to humans: people who are obese in mid-life are a whopping 74% more likely to develop dementia as they age (3), and shrinkage of the hippocampus is a hallmark of Alzheimer’s and other forms of dementia (4).Davidson suggests that the difficulty formerly obese people have in maintaining weight loss, could be partly due to permanent changes in the brain as a result of eating a saturated fat-rich, obesigenic diet for many years. Now, if you've been overweight for years and you're starting to feel just a little depressed about your prospects of permanent weight loss, I have some good news for you: there is an effective therapy that can literally rewire the brain, dramatically reduce levels of the hormone cortisol, which in excess causes the hippocampus to shrink, and completely transform your emotional response to the unhealthy foods you crave. Read all about it here.
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