Photo: Artificial Heart from Abiomed
Happy Valentine’s Day to all! I thought I’d add to the spirit of the day with a heart-related post.
I came across a very interesting study describing the utilization of different nutrients by the heart titled “Carbohydrate-enriched diet impairs cardiac performance by decreasing the utilization of fatty acid and glucose.” Abstract here.
The study by Porto et al, concluded that “a high-carbohydrate diet can damage myocardial contractile function by decreasing the cardiac utilization of glucose and fatty acids.” I interpreted this as the heart basically runs less efficiently when given more carbohydrates as fuel. I took away four key ideas, which I’ll get to in a second, from this study that provide food for thought.
Looking at the composition of the diets given over 9 days, one group (mice) received the “standard” diet of 39.5% carbohydrate, 8% fiber while the high-carbohydrate group got a 58% carbohydrate diet. This was interesting to me because I’m guessing many Americans eat a diet that is higher in carbohydrate than this every day. Contrast this with what I learned in medical school cardiac physiology, that free fatty acids (FFAs) were the “fuel of choice” for the heart.
So the main points of interest for me were:
1) The myocardium that was in the high carbohydrate milieu had decreased expression of lipoprotein lipase (LPL) – This is significant but fairly intuitive. When fed *carbohydrate* cells turn off their fat burning potential. This is powerful for people to realize that a high carb/low fat diet essentially handcuffs any effort to lose fat while exercising through a decrease in LPL activity.
2) Contractility, the squeezing power of the heart, decreases with higher carbohydrate intake. This follows what I learned in physiology, given inferior fuel, it follows that the muscle won’t work as well. However, taken a bit further, this has interesting implications for all people in athletics and older patients.
First, having played tennis in high school (while very overweight) and then in college (after losing about 100 pounds with a high fat diet) I can give you an interesting viewpoint. In high school, I followed the conventional wisdom, sitting down to spaghetti dinners before big matches or hockey games. I would feel sluggish and “doped” when I had to actually play in the next 24 hours. In college, I had switch to high fat meals pre-event, and I would feel “on-edge” (in a good way) and full of energy. It will be impossible to know which was responsible for the change in energy, the weight loss or diet change, but I feel it is interesting anyway. I gained aerobic capacity without significant training within a few months with just a diet change.
Second, the study lends itself to a hypothesis that a high fat diet may improve contractility in patients with Congestive Heart Failure (CHF). While taking care of these patients in medical school, I observed physicians who had little to do besides manage symptoms by placing patients on toxic/dangerous drugs to increase pumping function, using drugs to try and slow the decline of cardiac function, or ultimately put in a pacemaker to artificially increase contractile function. I would be interested to see how CHF patients do on a high fat, low carbohydrate diet, with echocardiography to measure cardiac contractility.
Stay with me for the final two, that I find most interesting…
3) The high carbohydrate group showed decreased GLUT4 mass and glucose uptake. Glucose Transporter 4 (GLUT4) is the insulin-regulated glucose transporter found in adipose tissues and striated muscle that is responsible for insulin-regulated glucose transport into cells. GLUT4 is expressed only in muscle (heart and big guns) and fat cells, the major tissues in the body that respond to insulin (James et al 1988). So extending the thought to all muscles and fat tissue in the body, a higher carbohydrate diet will lead to less GLUT4 in the membrane of the cells –> less insulin effect in total (insulin resistance) –> decreased usage of blood sugar. Isn’t that interesting that the carbohydrate that is responsible for insulin release and increased blood glucose also down regulates the receptor that is responsible for removal of the blood glucose? I would argue that the carbohydrate, insulin, GLUT4, and blood sugar system is there to be used only in certain “feast” times, not daily as seen with the SAD (standard American diet).
4) Last, the higher carbohydrate had impaired expression of the peroxisome proliferator-activated receptor α gene. What’s this PPARα thing? Well, it is a transcription factor, basically an on/off switch for getting DNA expressed into active cellular enzymes, that is present in many tissues including the liver, retina, kidney, heart, muscle, and fat tissue. Interestingly, a common class of dyslipedemia drugs and triglyceride-lowering agents (Fibrates) activate the PPARα receptor in the tissues listed above (mainly act on the liver). This activation of PPARα is known to (Barter et al 2006):
- Increase β-oxidation in the liver (Burn Fat)
- Decrease hepatic triglyceride secretion (Lower Triglycerides)
- Increase lipoprotein lipase activity, and thus increased VLDL clearance (Lower triglycerides and small, dangerous LDL cholesterol)
- Increase HDL (The Awesome Cholesterol)
New research (Hiukka et al 2010) also suggest that “PPARα activation attenuates or inhibits several mediators of vascular damage, including lipotoxicity, inflammation, reactive oxygen species generation, endothelial dysfunction, angiogenesis and thrombosis, and thus might influence intracellular signaling pathways that lead to microvascular complications.” The badness of diabetes (Heart Attack, Blindness, Kidney Failure, and Neuropathy) is avoided when PPARα is fired up. It seems like higher-carb diets may result in heart disease, diabetes, a whole host of inflammatory conditions, and stroke. Not saturated fat and high fat diets…(Thanks Minnesota’s own, Ancel…)
Wait, a higher carb diet did what to PPARα???
And wait, the ADA says : “There is no end in sight to the debate as to whether grains help you lose weight, or if they promote weight gain. Even more importantly, do they help or hinder blood glucose management? One thing is for sure. If you are going to eat grain foods, pick the ones that are the most nutritious. Choose whole grains. Whole grains are rich in vitamins, minerals, phytochemicals and fiber. Reading labels is essential for this food group to make sure you are making the best choices.
I’ll argue the end is in sight…this paper provides an interesting hypothesis as to how carbohydrates are responsible for weight gain, vascular complications, and dyslipidemia. The results suggest, the last thing we should do for high cholesterol (not a true problem anyway) is to lower our fat intake!
And so…Happy Valentine’s Day. Be good to your heart, eat fat, lower the carbohydrates, and move your muscles once in a while (muscle contraction moves GLUT4 to the surface of the cell to increase glucose usage.)
Have a great night.