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  Last updated: 11/27/2019

The Paleo Diet

Q. A local rider is preaching religiously on Paleolithic diet.. "doctors don't really know how to interpret blood tests........." One rider asked him - do you ride /run/swim faster? He replied he actually does not - but the guy does not rest explaining how toxic are grains for human being. Thoughts?

First are you using the Paleo diet to lose weight or as a health driven look at how you eat. The former is possible with any eating program that limits the Calories taken in, including the Paleo diet. I am going to focus on the nutritional aspects from the perspective of a diet change for an aerobic athlete (cyclist).

What is a Paleo diet?

It is a diet emulating what we think our hunter-gatherer ancestors ate. Paleo diets are low in sugar, refined carbohydrates, trans fats, and excess salt, all of which have been shown, in scientific studies, to be linked to poor health outcomes. At its simplest:

What is the science?

I'll go over Paleo diet assumptions point by point, but I think it is fair to say that the diet is based on very little science and a significant number of "logical leaps" associated with baseless assumptions. The evolutionary argument that humans are somehow maladapted to agriculture-based diets is one particularly unconvincing argument (resting on many unproven assumptions), yet it THE fundamental premise on which the Paleo diet bases its recommendations.

A major argument of Paleo proponents is that eating a low carbohydrate meal eliminates a rise in blood insulin levels. And insulin is the biggest health risk for those on a traditional balanced diet. The only problem is that the physiology does not support this. Although a major role of insulin is to move carbohydrates into the cell to be metabloized, protein and fats also stimulate insulin release from the pancreas. And protein is just as much a stimulant of insulin as pure sugar. A vegetarian diet is the only diet with a significantly lower overall insuin production.

And not only did it not protect from the potential health risks of a high blood insulin level, they added a risk factor with an increase in their LDL (low density - or bad - cholesterol).

Does it increase energy?

In a short answer, no. A quick survey the web (all personal observations and not a single controlled scientific studies) includes comments such as "I feel awesome. Although I am definitely lacking energy on the bike and I'm trying to wrap my head around eating so much fat and protein. I am ALWAYS hungry".

It fair to say that if you eat correctly, especially adequate carbohydrates to support high level aerobic activiy, you will not have any less energy. But there is no evidence that you will have more energy than on a well balanced traditional diet.

And if used incorrectly, that is the carbohydrate calories you take in are are not equal to what you need - basically you are now on a weight loss program)- you will develop the lack of energy that anyone on a carbohydrate restricted diet experiences.

Will you feel better?

That is the allegation the believers (actually closer to zealots) of the Paleo diet. Whether they had a unrealized food intolerance or are now experiencing a placebo response from taking what they see as a positive step for their own health is open to debate. And then you find a lot of comments such as "I love the Paleo diet, but have added back dairy as it makes me feel even better". So the bottom line here, to quote "Too many people are trying to fit the Paleo lifestyle into a "one size fits all" - not gonna work."

What's up with the avoidance of legumes and grains - and sugar?

Paleo proponents argue that legumes, grains, and other starches (i.e. potatoes) contain high levels of anti-nutrients (lectin, prolamin, phytate and saponins, for starters). These compounds, the Paleo philosophy holds, block key digestive enzymes, promote inflammation and, in some cases, lie at the root of autoimmune diseases and cancer. Is that true? Doubtful.

Sound scientific studies have shown that legumes and whole grains reduce risk of disease and improve insulin sensitivity and blood glucose levels - not to mention decrease BMI.

Consider that the Paleo diets does not allow for any grains or legumes. This pretty much eliminates many traditional cuisines including Japanese, Italian, Indian and Greek , and ignores the fact that these cultures include some of the world's healthiest and longest-lived individuals.

The problem is more likely processed foods with these components as global diets that exclude highly processed foods but include grains and legumes have been some of the most successful for health. Diseases of civilization become problematic in Western cultures where processed foods have replaced whole foods for a large proportion of the daily calories.

But the elimination of processed foods does touch one proven health benefit of a Paleo diet, eliminating the insulin surge that follows the eating of processed foods and sugars. Fructose (from fruits) is a much healthier approach as it blunts the insulin surge and fruits also include natural anti oxidants and other micronutrients. If you want to read more, look at glycemic index. But don't go overboard on the fructose as current data has linked obesity and the metabolic syndrome to the overuse of corn based fructose syrup in our society and the old saw that the overuse of any nutrient can have negative aspects.

A possible explanation of the benefits of the elimination of processed sugars is a more stable energy Levels. The Paleo diet relies heavily on whole meats, vegetables and fruits. These foods digest slowly, keeping blood sugar levels stable throughout the day. Stable blood sugar eliminates the energy and mood swings that can result from a diet high in processed carbs and refined sugar.

What about the evolution argument?

According to the Paleo-ists, the modern human digestive system hasn't evolved to handle the refined sugars, starchy carbs, grains, legumes, and dairy products that have snuck into our diets over the past 10,000 years. This is conjectural at best, and if one is going to use the evolutionary argument, humans and other great apes have been evolving for 20 million years, starting back in the Miocene era. And any evolutionary change at the very basic metabolic level would almost certainly take more than 10,000 years.

The need for large amounts of meat protein (the paleo argument) is refuted from an analysis of the protein content of breast milk. Although we can speculate endlessly (without hard data) about our ancestors diet on the savannah, the facts are much better inferred from an analysis of the protein content in breast milk. This is the source of nutrition that we all eat (exclusively) during the period of time in our lives that we were going thorough our most rapid growth (the first year). If there was an evolutionary advantage to more protein, those mothers with a higher protein concentration in their milk would have won the evolutionary race. And the protein content of breast milk? Less than 1%.

The "Paleolithic Diet" is speculation about a short segment of our evolutionary history, the last 10% of hominid evolution. What about the first 90%? If you really want to look at an "evolutionary diet" this link provides a nice summary of the most likely scenario.

And we have some pretty solid evidence to support that theory. Analysis of fecal waste from archaeolgic digs strongly suggests that "...for over 99% of our existence as a distinct species, our gastrointestinal tract has been exposed to the selective pressures exerted by a fiber-filled diet of whole plant foods. So, for millions of years before the first stone tools and evidence of butchering, our ancestors were eating plants."

This is an interesting article that suggests even the gladiators of Rome lived and fought on a carbohydrate rich, and mostly vegetarian rather than a meat based diet.

Our digestive enzymes are quite powerful, and not "evolved" to break down one type of food over another. The small intestine, where absorption takes place, sees only the final products of digestion as amino acids, fats, and simple sugars, the building blocks of all foods.

We should focus on defining the optimal ratio of these 3 building blocks in our diet along with eliminating potentially harmful oils and fats rather than focusing on the original form of the food that enters our mouth.

And if you want to argue meat versus plant, the bulk of the science suggests our ancestors existed on a plant based, not animal, diet - what we ate during more than 90% of our evolutionary history. And for the athlete, that means recognizing that high level aerobic performance (running from our ancestral enemies) developed with carbohydrates (and not protein) as the favored energy source.

Is the Paleo diet compatible with aerobic activities?

It is. The only drawback is that an unconscious limitation of carbohydrates can lead to low glycogen stores and chronic glycogen depletion with regular exercise. Even though it is difficult, you can compensate by eating more complex carbohydrates in the form of sweet potatoes, winter squash, and yams, especially if you are planning on an event of more than 90 minutes duration.

With fewer carbohydrates to rely on for energy, your body tends to tap into stored fat to make up the difference. But,and this is a big but, for aerobic activity a carbohydrate deficient diet and use of fat stores equals "bonk". Thus you cannot perform optimally if you do not actively focus on eating enough carbohydrates.

Although the normal Paleo diet follows an "unweighed and unmeasured" mindset, you can minimize the athletic risk (maximize energy levels and recovery times) by focusing on the total calories and composition of your daily diet. The percentages are similar to those recommended elsewhere on this website. to optimize energy levels and recovery times, the Paleo diet breaks down the recommended ranges for carbohydrates, protein and fat. Year-round protein consumption should be 20 percent to 25 percent of your total calories. The ratio of fat and carbohydrates will vary based on the training schedule. During the general preparation training period, fat calories should provide 30 percent of the total calories with 50 percent coming from carbohydrates. During peak training, an athlete has a greater demand for carbohydrates resulting in an increase to 60 percent of the calories from carbohydrates and 20 percent from fat.

The Paleo diet is a difficult one to follow.

The foods encouraged on the Paleo diet can be more expensive than foods allowed on other diets. The Paleo diet typically calls for grass-fed beef, free-range chicken and eggs, and fresh fruits and vegetables. Inexpensive foods like pasta, rice and bread are not allowed on the Paleo diet. Processed grains and dairy are widely used in prepared foods. They are also not allowed on the Paleo diet. Consequently, Paleo dieters often find it difficult to eat out or grab meals on the go. Fast food is often out of the question, as are most non-perishable options, excluding nuts.

And if you enjoy eating, consider the fact that you can never eat cheese or drink wine again and see how far you get subsisting on a Paleo diet.

If you currently eat a typical Western diet with little variety and many processed foods, do well diet plans, and have no qualms about giving up or modifying traditional meals to meet your dietary demands, then you will have better luck following the Paleo diet.

My bottom line:

Paleo dietary claims are mostly anecdotal with little basis in science. Take grains for example. Scientific studies looking at whole grains show a host of health benefits. You can also turn to the Okinawans or Sardinians that have carbs/whole grains as dietary staples, and yet they are among the longest living people on earth with the lowest rates of disability. Yet the Paleo diet says they are "toxic".

The diet does have the positive health benefits associated with an emphasis on fresh fruits and vegetables and its move away from sugar based drinks and foods. But the price is an added risk from a higher LDL (and its association with vascular disease). It is not a magic bullet to improve health by avoiding toxic carbohydrates.

Can you be a Paleo and a competitive cyclist? Yes. It will be difficult (a more restricted diet), more expensive, and force you to keep track of your carbohydrate calories. And if you are in the small group with chronic GI complaints, it may be worth a one month trila as an experiment.

Does it increase energy? There is no evidence to support that claim. It is fair to say that if you eat correctly, especially adequate carbohydrates to cover your athletic pursuits, you will not have any less energy. But there is no evidence that you will have more energy than on a well balanced traditional diet. And if used incorrectly, that is the carbohydrate calories you take in are are not equal to what you need - basically you are now on a weight loss program - you will develop the lack of energy that anyone on a carbohydrate restricted diet experiences.

For me, I like my wine with dinner and occasional cheese. And it would eliminate my favorite on the bike snack (fig newtons) and my favorite recovery drink - a Coke.


WHY VEGETARIANS HAVE LESS HEART DISEASE. - From a regular column I write for a local paper.

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?


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