Monday, August 17, 2020

Why vegetarians have less heart disease.


We know that those with diets higher in plant foods (and lower in animal foods) have a decreased risk of heart attack and stroke (as well as less diabetes and even cancer).

The favorite culprit is the high fat and cholesterol content of animal meats. A second is high-temperature cooking (pan-frying, grilling) producing cancer causing and other harmful intermediary compounds.

Although both may be contributing factors, more and more evidence is pointing to two proteins found in all red meat - carnitine and the cell sugar-protein molecule Neu5Ac - as the root cause of severe blood vessel disease.

Carnitine is a muscle protein. After digestion, carnitine absorbed and processed in the liver into trimethylamine (TMA) which is in turn modified by colon bacteria (our microbiome) into trimethyl n-oxide (TMAO).

In lab experiments, TMAO is directly toxic to blood vessel lining cells. The injured cells absorb fats from the circulation which results in the formation of blood vessel plaques, and in the presence of high blood fat and cholesterol levels, the process is accelerated.

A clinical parallel has been identified in studies on patients seen in hospital ERs for chest discomfort. Those with the highest blood levels of TMAO (compared to the lowest) are  six times as likely to die within the following month and twice as likely to die within seven years.

Vegetarians as a group have the lowest average blood levels of TMAO. Interestingly, when given a single dose of carnitine (a piece of steak) their blood TMAO levels barely budge. The reason? A person's microbiome responds to their diet. Expose the colon bacteria to more of a specific food and those that thrive on it multiply. Being exposed to only small amounts of carnitine in a no-meat diet, there are very few carnitine metabolizing bacteria available to process that occasional steak. This suggests that an occasional meat containing meal should be less harmful to your blood vessels than when it is part of your daily diet.

The second meat protein is Neu5Gc, a cell surface protein found on all non human mammalian cells (but not chicken or fish). Eons ago a genetic mutation in humans led to its modification to a similar molecule (Neu5Ac). As this new protein provided some protection against malaria, it became the dominant form.

Our immune system recognizes invading germs by their cell surface proteins. When it detects proteins that are different from our own, antibodies to kill the invading germs are produced.

With this change in our cell sugar-protein, the immune system now sees all non human mammal meat as “different”, the immune system revs up, and antibodies are formed. The result is that those who regularly eat beef (a mammal meat) have blood markers reflecting a state of chronic inflammation.

A side effect of the overactive immune system is collateral damage to cells throughout the body. In the blood vessels this means more atherosclerosis with an increased risk of heart attacks and strokes, and in other cells the damage increases the risk of cancer.

Supportive evidence once again comes from the laboratory where mice, genetically altered with the human gene mutation and placed on a meat diet have twice the heart attack risk of genetically unmodified mice on a similar diet.

These two harmful effects of a mammal meat diet are moderated to a degree by small molecules produced from the metabolism of fiber by our microbiome. But with most red meat containing diets being lower in fruits,vegetables and whole grains, this protection is weakened. The effect is observed in those on a strict paleo diet (high red meat and no whole grain) who have much higher blood TMAO levels than those who eat even a small amount of whole grain.

What does this body of work suggest as far as healthy diet changes?

First, cut red meat intake and decrease exposure to the toxic effects of TMAO. In one large study, there was a 10% (one in ten) decrease in heart disease deaths in those who cut their red meat intake to an average of half a serving per day! Alternatives to be considered are poultry, fish, nuts, legumes, low-fat dairy, and whole grains.

Second is to take advantage of the protective effects of fiber. The benefits of additional servings of fruits and vegetables have been shown to increase up to 10 servings per day.

Finally, it is never too late to make a change. Health professionals who began eating more whole grains, fruits, vegetables, and fish were able to significantly lower their risk for death in as few as 8 years.

References




















Egg and cancer risk via TMAO

Nice summary of non heart disease risks of TMAO https://nutritionfacts.org/video/can-vegan-fecal-transplants-lower-tmao-levels/ 
Posted by at No comments:

Sunday, January 19, 2020

Fat metabolism and the ketogenic diet


Fats provide 20 to 40% of the calories in an average daily American diet.

More than 95% of dietary fat is in the form of triglycerides which are a combination of three fatty acid (FA) molecules and a single glycerol molecule. The other 5% is cholesterol and phospholipids. Triglycerides are an important energy source while the cholesterol and phospholipids are important as building blocks for cell growth.

In the small intestine, triglycerides are cleaved into their component molecules – glycerol and fatty acids. The fatty acid molecules are then transported through the intestinal lining cells into the blood. As they circulate, they diffuse through cell membranes throughout the body where they are either directly metabolized as an energy source or reconstituted into triglycerides for storage for future use.

The bulk of the body's 50,000 – 60,000 stored fat calories are in fat cells (lipocytes) with 2,000-3,000 additional calories stored in liver and muscle cells.

Both fatty acids and glycogen (the storage form of carbohydrates) are metabolized into the same energy containing compound, Adenosine Triphosphate (ATP), to provide energy for the body's cells.

Decades of research suggested that a diet low in fat, with the bulk of daily calories from carbohydrates, was the healthiest diet. But in the past few years that recommendation has come into question.

Instead it's been found that replacing carbohydrate calories with fat calories may be the healthier approach, actually increasing HDL (good cholesterol) which suggests less long term cardiovascular disease.

 And dieting with 33% of daily calories from fat was actually a more effective long term weight loss strategy than a diet with fats limited to only 20% of daily calories.

If that's the case, why all the interest in a ketogenic diet?

The basis of both the Atkins low carbohydrate and the more severely carbohydrate restricted ketogenic diet was speculation that the combination of carbohydrate restriction, combined with calorie restriction, would force the body to turn to fatty acid metabolism for energy and in turn increase the rate of fat (weight) loss.

When there are inadequate carbohydrate calories available, we know cells use fat to power cells with the metabolic end product being ketones. This occurs overnight, when fasting, and in diabetics where carbohydrates cannot get into the cells. The cells turn to fat for fuel, and the patient becomes ketotic with an acetone (a ketone) smell on their breath.

Although logic supports the ketogenic argument, the ultimate outcome is not what we would predict.

Initially, a ketogenic diet gives dramatic results. On a standard calorie restricted diet, a study group lost about a pound a week. Switched to a ketogenic diet this increased to 3 ½ pounds in the first week.

But further investigation of their body composition found that the rate of fat loss had decreased by 50% with the bulk of the extra weight loss from water weight. It appeared that the with carbohydrate restriction, the body began cannibalizing its own protein for energy instead of using fat. The group lost less fat and more protein (and water).

In a real life scenario, a group of CrossFit trainees switched to a ketogenic diet based on the assumption that a switch to a fat based metabolism would help their endurance performance. They found their leg muscles shrank by 8%. Not the trade off they were expecting.

The moral to the story? Fats, protein, and carbohydrates all have a place in a healthy diet. Your body evolved to use carbohydrates to fuel muscle activity. While excess carbohydrates beyond those needed for daily activities are converted into fat, too few are also a problem as the body scavenges needed energy from the protein of its own cells.

References:

http://www.cptips.com/fat.htm

https://journals.sagepub.com/doi/pdf/10.1177/0310057X1804600506  Ketosis with fasting

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5309297/   Ketones and exercise, with good set of references.

https://onlinelibrary.wiley.com/doi/full/10.1002/(SICI)1520-7560(199911/12)15:6%3C412::AID-DMRR72%3E3.0.CO;2-8?sid=nlm%3Apubmed  Ketone metabolism.
Posted by at No comments:
Subscribe to: Posts (Atom)