In 2003, Dr. Robert Lustig saw a six year old Latino boy in his clinic in Salinas, California. Juan weighed 100 pounds and was wider than he was tall, but his mother insisted he ate a healthy diet. When Dr. Lustig began to look more closely, Juan’s diet did seem ok for a growing boy; however, through his directed questions, Dr. Lustig found the somewhat unexpected culprit: orange juice. Juan had gotten into the habit of drinking an entire gallon of orange juice per day. This is approximately 1,760 calories and 336 grams of sugar, which is over 1 cup of sugar. Additionally, the amount of dietary fiber: 0 grams. Why was Juan doing this? Because the government provided it to his family for free, and his mother had no idea how harmful it could be to her son’s health. In fact, she felt that the more he drank, the more nutrients he was getting.
Although obesity has received a lot of media attention in the last few years, I was still floored by some of the statistics in Fed Up, a documentary I recently watched (and highly recommend). I was surprised that the focus was around the role sugar plays in the growing epidemic, a definite shift from the more common topics of saturated fat and exercise. The numbers get a little scary:
In the United States, it is estimated that 93 Million Americans are affected by obesity.
Kids watch an average of 4000 food-related ads every year (10/day).
A 20-ounce bottle of soda contains the equivalent of approximately 17 teaspoons of sugar.
It will take a 110-pound child 75 minutes of bike riding to burn off the calories in one 20-ounce bottle of soda.
In 2012, Americans consumed an average of 765 grams of sugar every 5 days, or 130 pounds each year.
We all know that the Western Diet, characterized by high saturated fat and refined sugar, has been implicated in a range of diseases such as type 2 diabetes, cardiovascular disease, and stroke, but do we know whether and how this diet is affecting our brain?
We start the quest for an answer to our question with a small neural structure called the hippocampus, named after the greek words hippos and kampos meaning “horse” and “sea monster” respectively. This is because of the structure’s unusual shape and appearance. Do you see the resemblance?
Much work has been done to try to understand this structure (and it happens to be the one that Henry Molaison had removed in the 1950’s-see About Gray Matters for more on this story). It is heavily implicated in memory, and more specifically, important for those memories involving spatial cues such as remembering how to navigate around your house. Because the hippocampus contains unusually large cells, it is particularly vulnerable to environmental insults, including things such as diet.
What protects the hippocampus from environmental toxins?
The blood brain barrier is a crucial component of the nervous system. It serves as a gate keeper who “decides” what unwanted components of the blood must stay out and which nutrients will be allowed in, protecting the brain from harmful substances.
If you think about a football stadium with entrances surrounding its periphery, the blood brain barrier would be like the people checking tickets. Only those with tickets would be allowed in. Now think about what might happen at the super bowl if many of those ticket checkers were just not there. People without tickets would start hopping over the barriers and entering the stadium to view the game for free. This is what happens when there is damage to the blood brain barrier: unwanted substances get into the brain.
So how does this answer our question about how Western Diet affects the brain?
Recent research has revealed two important trends:
1. Western Diets seem to stimulate intestinal production of a protein found in the body called amyloid-β.
2. Elevated levels of amyloid-β proteins have been shown to damage the blood brain barrier in rats.
Why does this matter?
One of the hallmark signs of a brain diseased by Alzheimer’s is the presence of plaques, particularly in the hippocampus. These plaques can be thought of as dangerous junk, cluttering the cell and disrupting normal function, and they are partially caused by the accumulation of amyloid-β proteins. Starting to see how this story is coming together?
Based on the current evidence, we can start to form a theory: A Western Diet increases bodily levels of amyloid-β protein, leading to increased amyloid-β levels in the blood. This elevation could contribute to blood brain barrier damage (equivalent to losing those ticket checkers!), resulting in more amyloid-β (ticketless individuals) being able to get into the brain. Once in the brain, these proteins can damage the large cells in the hippocampus, which are particularly vulnerable. The theory is laid out nicely in this diagram:
(1) Western Diet results in (2) elevated levels of amyloid-β (Aβ) from the small intestines, (3) thus increasing Aβ levels in the vascular system. (4) High levels of Aβ contribute to blood brain barrier damage, (5) which leaves the hippocampus (HPF) vulnerable to damage by Aβ.
So this leaves us with the possibility that obesity and dementia potentially share a common contributory factor: overconsumption of foods high in saturated fatty acids and simple sugars, or the Western Diet. Given the statistics about the prevalence of obesity in this country and others, the possibility that these people are also at a higher risk for future dementia is incredibly concerning.
Although not many people drink a gallon of juice every day, I have to admit that before reading Dr. Lustig’s book and watching Fed Up, I went out of my way to drink orange juice because I thought it was healthy for me. I did not realize how much sugar was in it! Now I just eat the fruit. I hope this will be better for my body and my brain in the long run.
For more information about the role sugar plays in the obesity epidemic, I recommend:
1. Fat Chance: The bitter truth about sugar by Robert Lustig
2. Fed Up Documentary (more information found here: http://fedupmovie.com/#/page/about-the-issue?scrollTo=facts)