Paleo vs. Vegetarian Diets; Fats vs. Carbs

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Ask the Dietitian: Finding the best fuel



Vegetarian and Paleo diets seem to be equally popular and totally at odds. Is there any nutrition science to support one over the other, or does it simply come down to personal experimentation and experience?

—Martin Miller, Helena, Montana

A vegetarian diet is devoid of red meat, poultry and often fish, but includes animal byproducts such as cheese, milk and eggs. Studies have shown that vegetarians live longer than their carnivorous counterparts because the diet is generally high in dietary fiber and low in saturated fat. There is a widespread concern that a vegetarian diet is deficient in protein, vitamin B12 and iron—all key nutrients for a trail runner’s well-being. However, by eating a varied diet with adequate calories, most people will find that they can easily consume enough of these nutrients, in the form of of leafy greens, fruits and vegetables, fortified cereals, whole grains, lentils, seeds and nuts.

In contrast, the Paleo diet consists of meat, fish, shellfish, poultry, eggs, vegetables, tree nuts, fruits and berries. The theory behind the Paleo diet is that the addition of grains, legumes and dairy to the human diet precedes and contributes to chronic diseases like obesity, heart disease and diabetes. The Paleo diet is low on carbohydrates, the MVP in a long-distance runner’s diet. In a previous Trail Runner article, the benefits of the Paleo diet for trail runners are highly praised by Joe Friel and Dr. Loren Cordain. In their book, The Paleo Diet for Athletes, these Paleo advocates have modified the diet in order to meet the needs of the modern-day distance runner. They say our ancestors “put in about 10 miles, which included walking, slow running and short bursts of speed.” There were also times when they went for days with no exercise. The modifications they suggest essentially throw out the Paleo rules prior to, during and after a race, hard workout or run longer than 10 miles. Friel and Cordain recommend that a Paleo athlete follow the same rules as other Non-Paleo athletes at these times by consuming foods rich in carbohydrates and fueling with traditional sports drinks, gels and energy bars.

Both a vegetarian and Paleo diet may inherently enhance runners’ health and performance by increasing consumption of nutrient-packed foods like fruits and vegetables over the typical American diet of processed foods, refined carbohydrates and sugars, but each diet carries its own risk for nutrient deficiencies, given there are major food groups excluded in each. Experiment with what you enjoy eating most and what foods help your body thrive in athletic performance. The goal is to have a well-rounded diet that is void of nutrient gaps and sufficient in calories to ensure that your body is getting everything it needs to train, race and recover efficiently. A nutritionist or dietitian can help you monitor for signs of potential nutrient deficiencies.


What is better for fueling a long run—fats or carbohydrates?

—Question paraphrased from similar questions submitted by several readers.

Carbohydrates and fats are a major source of energy for endurance athletes. Unfortunately, we only have about 2000 calories worth of glycogen, or stored carbohydrates, reserved in our muscles, liver and blood glucose. To prevent low blood sugar and its debilitating effects, consuming carbohydrates is necessary for runs or races that last longer than 90 minutes. The benefits of ingesting carbohydrates like maintaining proper blood glucose levels, delaying the onset of fatigue and preventing muscle glycogen depletion are well supported by decades of research with endurance athletes.

Because we have a nearly unlimited supply of calories from fat stores, it is unnecessary to replenish that fat during a run. In addition, most studies show that consuming fat while running does not increase fat burning or spare the use of glycogen. It takes more energy to process fat than it does to process carbohydrates. Any gain in calories would be lost and, because fat is slow to digest, there is a chance that it will lead to an upset stomach.

Medium-chain triglycerides (MCTs) are fats that are absorbed rapidly by the body and, like carbohydrates, are a quick source of energy. MCTs such as coconut oil are becoming more popular as an alternative to carbohydrates during ultra events to help satiate hunger and avoid flavor fatigue from an excessive intake of sweet gels and drinks.

As you become more aerobically fit, your body becomes more efficient at using its existing fat stores as fuel. The ability to burn fat stores efficiently not only improves endurance capacity by sparing glycogen, but also reduces the need to rely on eating carbohydrates or fat during a run, which decreases the risk of intestinal distress and a consequent decrease in performance.


Editor’s Note: This is an installment in our online Ask the Dietitian column with Maria Dalzot, MS, RD, CDN and an avid trail runner. You can visit her blog at and submit your nutrition questions to

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