Paleolithic Diet Clinical Trials Part III

I'm happy to say, it's time for a new installment of the "Paleolithic Diet Clinical Trials" series. The latest study was recently published in the European Journal of Clinical Nutrition by Dr. Anthony Sebastian's group. Dr. Sebastian has collaborated with Drs. Loren Cordain and Boyd Eaton in the past.

This new trial has some major problems, but I believe it nevertheless adds to the weight of the evidence on "paleolithic"-type diets. The first problem is the lack of a control group. Participants were compared to themselves, before eating a paleolithic diet and after having eaten it for 10 days. Ideally, the paleolithic group would be compared to another group eating their typical diet during the same time period. This would control for effects due to getting poked and prodded in the hospital, weather, etc. The second major problem is the small sample size, only 9 participants. I suspect the investigators had a hard time finding enough funding to conduct a larger study, since the paleolithic approach is still on the fringe of nutrition science.

I think this study is best viewed as something intermediate between a clinical trial and 9 individual anecdotes.

Here's the study design: they recruited 9 sedentary, non-obese people with no known health problems. They were 6 males and 3 females, and they represented people of African, European and Asian descent. Participants ate their typical diets for three days while investigators collected baseline data. Then, they were put on a seven-day "ramp-up" diet higher in potassium and fiber, to prepare their digestive systems for the final phase. In the "paleolithic" phase, participants ate a diet of:

Meat, fish, poultry, eggs, fruits, vegetables, tree nuts, canola oil, mayonnaise, and honey... We excluded dairy products, legumes, cereals, grains, potatoes and products containing potassium chloride...

Mmm yes, canola oil and mayo were universally relished by hunter-gatherers. They liked to feed their animal fat and organs to the vultures, and slather mayo onto their lean muscle meats. Anyway, the paleo diet was higher in calories, protein and polyunsaturated fat (I assume with a better n-6 : n-3 ratio) than the participants' normal diet. It contained about the same amount of carbohydrate and less saturated fat.

There are a couple of twists to this study that make it more interesting. One is that the diets were completely controlled. The only food participants ate came from the experimental kitchen, so investigators knew the exact calorie intake and nutrient composition of what everyone was eating.

The other twist is that the investigators wanted to take weight loss out of the picture. They wanted to know if a paleolithic-style diet is capable of improving health independent of weight loss. So they adjusted participants' calorie intake to make sure they didn't lose weight. This is an interesting point. Investigators had to increase the participants' calorie intake by an average of 329 calories a day just to get them to maintain their weight on the paleo diet. Their bodies naturally wanted to shed fat on the new diet, so they had to be overfed to maintain weight.

On to the results. Participants, on average, saw large improvements in nearly every meaningful measure of health in just 10 days on the "paleolithic" diet. Remember, these people were supposedly healthy to begin with. Total cholesterol and LDL dropped, if you care about that. Triglycerides decreased by 35%. Fasting insulin plummeted by 68%. HOMA-IR, a measure of insulin resistance, decreased by 72%. Blood pressure decreased and blood vessel distensibility (a measure of vessel elasticity) increased. It's interesting to note that measures of glucose metabolism improved dramatically despite no change in carbohydrate intake. Some of these results were statistically significant, but not all of them. However, the authors note that:

In all these measured variables, either eight or all nine participants had identical directional responses when switched to paleolithic type diet, that is, near consistently improved status of circulatory, carbohydrate and lipid metabolism/physiology.

Translation: everyone improved. That's a very meaningful point, because even if the average improves, in many studies a certain percentage of people get worse. This study adds to the evidence that no matter what your gender or genetic background, a diet roughly consistent with our evolutionary past can bring major health benefits. Here's another way to say it: ditching certain modern foods can be immensely beneficial to health, even in people who already appear healthy. This is true regardless of whether or not one loses weight.

There's one last critical point I'll make about this study. In figure 2, the investigators graphed baseline insulin resistance vs. the change in insulin resistance during the course of the study for each participant. Participants who started with the most insulin resistance saw the largest improvements, while those with little insulin resistance to begin with changed less. There was a linear relationship between baseline IR and the change in IR, with a correlation of R=0.98, p less than 0.0001. In other words, to a highly significant degree, participants who needed the most improvement, saw the most improvement. Every participant with insulin resistance at the beginning of the study ended up with basically normal insulin sensitivity after 10 days. At the end of the study, all participants had a similar degree of insulin sensitivity. This is best illustrated by the standard deviation of the fasting insulin measurement, which decreased 9-fold over the course of the experiment.

Here's what this suggests: different people have different degrees of susceptibility to the damaging effects of the modern Western diet. This depends on genetic background, age, activity level and many other factors. When you remove damaging foods, peoples' metabolisms normalize, and most of the differences in health that were apparent under adverse conditions disappear. I believe our genetic differences apply more to how we react to adverse conditions than how we function optimally. The fundamental workings of our metabolisms are very similar, having been forged mostly in hunter-gatherer times. We're all the same species after all.

This study adds to the evidence that modern industrial food is behind our poor health, and that a return to time-honored foodways can have immense benefits for nearly anyone. A paleolithic-style diet is a very effective way to claim your genetic birthright to good health. Just remember to eat the organs and fat. And skip the canola oil and mayonnaise.

Paleolithic Diet Clinical Trials
Paleolithic Diet Clinical Trials Part II
One Last Thought

Flu Season is Here

I just checked Google Flu Trends and flu season is upon us. It's time to tighten up your diet, find a good source of vitamin D and avoid sick people. Avoid sugar, industrial vegetable oil and processed food in general as they lower immunity. If you feel like you're coming down with something, consider fasting to nip it in the bud. It works for me.

Low Stomach Acid and Nutrient Absorption

As I mentioned here and here, low stomach acid (hypochlorhydria) causes many problems, including bacterial overgrowth in the small intestine, lowered resistance to infection by ingested pathogens, an increase in gastric cancer susceptibility, and reduced nutrient absorption. It has the potential to underlie many other issues, including food sensitivities. The prevalence varies by age, increasing from less than 10% in the young to over 50% in the elderly.

In a previous post, I mentioned a few nutrients I had come across that require full stomach acidity for optimum absorption. I recently found a nice paper from 1989 titled "Hypochlorhydria: a Factor in Nutrition", which broadened my perspective. Here's a revised list of nutrients known to be affected by hypochlorhydria, as of 1989:

• Calcium
• Iron
• Folic acid
• Vitamin B6
• Vitamin B12
• Vitamin A
• Vitamin E
• Niacin
• Protein

That's a hefty list, and it's not even comprehensive!

Cranial Development in Nepal, etc.

I saw a great movie on Saturday called "The Sari Soldiers". It's a documentary about the bloody three-way struggle between the Nepalese monarchy, Maoists, and political parties that ended with the dissolution of the monarchy in 2008. It's shot from the perspective of several very strong women affected by wartime atrocities.

I was getting on my friend's nerves during the movie because I couldn't stop commenting on the beautiful teeth, broad faces and great skin nearly everyone had. These were not actresses, they were regular people. They almost all had straight teeth and broad dental arches. I came to realize during the movie that people who have a great smile typically have a broad dental arch. There's something about seeing that wide, straight row of front teeth that attracts us. Here's a shot of one of the main characters (click for a larger view):

The Maoist army claimed to be 40% women. They were marching with heavy sacks and rifles all over the countryside, fighting the royal Nepalese army. That's no job for the feeble.

Of course, I had to look up Nepalese food as soon as I got home. It centers around rice, legumes and dairy, with a few spices, some vegetables and a modest amount of meat. Their primary fats are ghee (clarified butter) and yak butter. The national dish is called dal bhat, which means "lentils and rice". Here's one of the first recipes I found in a Google search:

Plain Rice (Bhat)
2 cups rice (Basmati or Long grain preferred)
4 cups (1 lt) water
1 tsp butter (optional)

Lentils (Dal)
1� cups lentil (any kind)
4 to 5 cups of water (depends preference of your consistency of liquid)
� tsp turmeric
1 tsp garlic, minced
6 tbsp clarified butter (ghee)
3/4 cup sliced onions
2 chillies (dried red chilies preferred) (depends on your preference)
Salt to taste

OPTIONAL
� tsp (pinch) asafetida
� tsp (pinch) jimbu
1 tbsp fresh ginger paste

Rice:

Wash rice and soak for 5 minutes.

Wash rice and soak for 5 minutes.

Boil the rice over medium heat for about 10 -15 minutes. Stir once thoroughly. Add butter to make rice give it taste as well as make it soft and fluffy.

Turn the heat to low and cook, covered, for 5 more minutes until done

Lentils:

Wash lentils and soak lentil for 10 minutes.

Remove anything that float on the surface after it and drain extra water.

Add drained lentils in fresh water and bring to a boil again. Add all spices.

Reduce the heat and simmer, covered, for 20 to 30 minutes until lentils are soft and the consistency is similar to that of porridge.

In a small pan heat the remaining of butter and fry the onions, chilies and garlic.

Stir into the lentils few minutes before you stop boiling. Serve with rice.

Did you catch the quantity of butter it calls for? 6 tablespoons of ghee and a tablespoon of butter! By my calculations, that's 784 calories worth of dairy fat for a 3,124 calorie dish, or about 25% butter by calories. I'd be willing to bet their butter is not the anemic industrial variety. With the amount of vitamin K2 MK-4 their diet is providing, it's no wonder their dental arches and teeth look so good. I'm sure not everyone can afford to eat that quantity of butter, but it's clearly a staple food in Nepal.

That recipe would typically be made with split lentils, which it's not critical to soak (although I still do). Recipes that called for whole lentils typically recommended a long soak before cooking.

Nearly everyone in the movie had great skin as well. Even the older people had nice skin. It was wrinkled, but firm and smooth between the wrinkles. Yet another feature of healthy cultures. Take a look at chief Sealth of the Suquamish and Duwamish tribes at 78 years old (photo taken in 1864). He's the city of Seattle's namesake. He lived most of his life as a hunter-gatherer in the Pacific northwestern United States:

OK, it's not the sharpest picture, but I think it's clear his skin is relatively smooth and firm for a 78-year-old. The object on his knee is the tribe's traditional reed hat.

I'll leave you with a quote from a book I'm currently reading, Paleopathology at the Origins of Agriculture:

Dental crowding should be indicative of nutritional or other chronic, severe stress since teeth will be less affected by chronic stress than alveolar bone size. Widdowson and McCance (1964) have demonstrated this effect in undernourished piglets and Trowell and co-workers (1954) have noted increasing crowding and impacted molars in severely malnourished children. Increased dental crowding may be indicative of severe and chronic stress in archaeological populations. However, we are unaware of the use of this potential indicator in any evaluation of health in prehistory.

So in archaeological sites, dental crowding is "indicative of nutritional or other chronic, severe stress", but in modern populations it's a fact of life? I think this is a testament to how resistant people are to coming to logical conclusions that challenge cultural norms.

More Thoughts on Hydrogen Gas and Bacterial Overgrowth

It's probably not a coincidence that H. pylori lowers stomach acidity. It's trying to feed itself. Lowering stomach acidity promotes poor digestion and extra food for hydrogen gas (H2)- producing bacteria further down the digestive tract. H. pylori thrives on the resulting increase in H2. There are countless examples in nature of parasites manipulating hosts to get what they want. A pretty simple example is Bordetella pertussis, the bacterium that causes whooping cough. It secretes factors that irritate the trachea, causing the victim to cough and thus facilitating its own spread through airborne droplets.

H2 is a high-energy molecule. In fact, it's being considered as an automobile fuel. It's also very small, allowing it to diffuse away from the digestive tract and throughout the tissues. Overproducing H2 in the digestive tract creates an all-you-can-eat buffet for whatever bacteria are present in the body that are capable of using it. As I mentioned in the last post, these bacteria include H. pylori, Salmonella and perhaps Clostridium. Nature abhors a vacuum. I'm sure there are organisms happy to siphon off some of this fuel. The interior of the body is relatively sterile, but there are plenty of bacteria hanging around the mucous membranes (nasal cavity, digestive tract, urogenital tracts) that could potentially exploit this energy source.

How do we thwart H. pylori and take back control of our stomachs? There are a few options. The first is to send in the big guns and take antibiotics. This is the standard treatment and it's usually effective, but I'm generally against antibiotics unless absolutely necessary due to their long-term effects on beneficial gut flora. Then there are other treatments like mastic gum, peppermint, gentian and probiotics, which may or may not be effective.

But the method I like best is starvation (of H. pylori). Obviously, the first step is to eliminate excess fructose, wheat, and anything else that causes digestive upset and gas. Several commenters on the last post mentioned that eating a "paleolithic"-type diet improved their digestion and reduced gas. That makes perfect sense to me, and it may actually be a very important effect of that type of diet. The same goes for low-carbohydrate diets. Two other weapons of intestinal flora starvation are chewing thoroughly and avoiding liquids during meals. The former allows you to absorb the maximum amount of calories from your food as rapidly as possible, leaving less for the bacteria. The latter makes digestion more effective by keeping stomach acid concentrated. A little bit of liquid such as a small glass of wine is probably fine.

If necessary, the next step may be to restore full stomach acidity, further cutting off the supply of H2 to H. pylori and breaking the cycle of reduced acidity, leading to increased H2, leading back to increased H. pylori growth. Sufficient stomach acid may also inhibit H. pylori directly, but there isn't much research on this. Restoring stomach acidity is pretty easy to do using betaine HCl supplements. Many people report improved digestion when they use betaine HCl. These basically release hydrochloric acid into the stomach, lowering pH. Most of them also contain pepsin, a protein-digesting enzyme secreted by the stomach. Buy them in capsule form rather than tablets so they dissolve rapidly.

Ideally, you should have your stomach pH checked to confirm you have insufficient stomach acidity before taking betaine HCl. If it's not lacking, there's no point in taking it (although trying it won't do you any harm beyond a little discomfort). But if you want to skip the expense, there are web pages that can teach you how to use subjective measures to determine if it's helpful for you. Some people feel that the stomach eventually "learns" to produce enough HCl again after a course of betaine HCl, after which they can stop taking it. This may reflect a suppression of H. pylori.

I think it's notable that healthy traditional cultures that ate plant foods didn't do it haphazardly. First of all, they typically ate the minimum amount of fiber necessary to get their calories. If they could remove fiber from their food, they did. For example, ogi is a widespread grain porridge eaten in Western Africa. To make it, you soak millet, corn or sorghum overnight. Then you pound it, mix it with water and strain it through a sieve. This removes the bran but allows most of the suspended starch through. The bran is fed to the animals, while the starch is fermented, cooked and eaten.

This is typical of healthy non-industrial cultures. They don't care about the glycemic index of starches, they care about maximizing digestibility and assimilation. In the process, they are minimizing food for their digestive flora. Fermenting grains before cooking may also reduce the amount of food left for gut bacteria. Starchy tubers and fruit (plantain, breadfruit) are also common features of healthy traditional cultures. They cook them thoroughly, sometimes mash them, and sometimes ferment them as well (e.g., poi).

Low-calorie vegetables are not staple foods in most of the world's healthiest non-industrial cultures, including hunter-gatherers. That's the main reason why I'm skeptical of the claim that eating immoderate quantities of vegetables is essential for health.

I do think it's worth mentioning that although they tried to minimize fiber, many (but not all) healthy non-industrial cultures nevertheless ate a lot of it and did just fine. It was inescapable for many of them. If you don't have the technology to remove rice bran, you have to eat it along with the starch. It may be just as well. Bran carries a disproportionate amount of vitamins and minerals. But it also comes along with a disproportionate share of toxins, which must be inactivated prior to eating by soaking, sprouting or fermentation. Healthy grain-based cultures knew this well, but we seem to have forgotten it in modern times.

Sugar, Hydrogen, Bacteria and Maldigestion

There are several ways to cause a nutrient deficiency. The first is to eat too little of a nutrient. Another way is to burn through your body's nutrient stores at an accelerated rate, for example, what omega-6 vegetable oils do to vitamin E, and what wheat bran does to vitamin D. A third way is to eat enough nutrients but fail to absorb them efficiently.

A good way to reduce your absorption of nutrients is to lower your stomach's acidity. This will protect you from those pesky nutrients protein, vitamin B12, and iron (and probably others as well). The stomach is one tough organ. When it receives food, a healthy stomach lowers its pH to roughly 2.0 by secreting hydrochloric acid. That's more acidic than lemon juice and more than 10 times more acidic than vinegar. This begins to break food down, and will kill most bacteria and other pathogens. Stomach acidity is basically the body's way of "cooking" food before further digestion. At the same time, the stomach secretes pepsin, which is an acid-stable enzyme that digests protein.

Insufficient stomach acidity promotes bacterial overgrowth in the small intestine and allows undigested proteins into the intestine. The gastrin knockout mouse, which is incapable of producing stomach acid, suffers from bacterial overgrowth, inflammation, damage and precancerous polyps in its intestines. The same thing happens when you treat mice with a drug that inhibits stomach acidification.

There are a few different ways to reduce your stomach's acidity level. The most straightforward is to take an antacid, or any number of drugs that lower stomach acidity (as in the mouse study above). But can we do it naturally? Sure, all it takes is a little Helicobacter pylori infection! Luckily, most people already have one.

H. pylori is a bacterium that's the main proximal cause of stomach ulcers. Antibiotics are now the standard treatment for ulcers, and they're effective. Treating an asymptomatic H. pylori infection with antibiotics increases stomach acidity, suggesting that H. pylori is capable of suppressing the secretion of stomach acid. In another study, eradicating H. pylori with antibiotics improved nearly all patients suffering from hypochlorhydria (insufficient stomach acid).

Like any organism, H. pylori likes to stay well-fed. Its favorite food is hydrogen gas (H2), and the more it gets, the more it grows. It's not the only bacterium to like H2. Salmonella, of food poisoning fame, requires H2 to become pathogenic. Clostridium bacteria are also associated with elevated H2. H2 is produced by the fermentation of food by bacteria in the digestive tract. It's very small so it diffuses around the body, reaching the stomach lining where it's eagerly gobbled up by H. pylori. It may be equally good food for a number of other parasites around the body.

Now let's stop beating around the bush and get to the meat of this post. It's all summed up in a beautiful title: Fructose Intake at Current Levels in the United States May Cause Gastrointestinal Distress in Normal Adults. Dr. Richard W. McCallum et al. fed doses of isolated fructose to 15 normal adults. Can I say it any better than the abstract?

More than half of the 15 adults tested showed evidence of fructose malabsorption after 25 g fructose and greater than two thirds showed malabsorption after 50 g fructose... Fructose, in amounts commonly consumed, may result in mild gastrointestinal distress in normal people.

Here's where it gets really interesting. One of the measures of malabsorption they used was H2 on the breath. Both the 25g and the 50g doses caused a large increase in H2, especially the 50g dose (5-fold increase). This is the same thing you see in people who are lactose intolerant. Bacterial fermentation is the only significant source of H2 in the human body. That means the fructose was hanging around in the small intestine for long enough to be decomposed by the local bacteria, who took advantage of it to proliferate.

Certain types of fiber also promote H2 production. Resistant starch, as well as certain non-caloric sweeteners, are readily fermented into H2 in some people. Cellulose, the predominant fiber in vegetables and grains, does not increase H2. The large difference in fiber content of rural vs. urban Mexican diets doesn't seem to correlate with H2 production by intestinal bacteria. Interestingly, both white and whole wheat bread increase H2 production.

Let's put those doses of fructose into perspective. One medium banana contains about 7 grams. A 16-ounce bottle of apple juice contains about 30 grams. A slice of cake contains about 12. One "child-size" 12 ounce cup of Coca-Cola from McDonald's contains 17 grams (as long as you don't get a refill!). One large 32 ounce Coca-Cola contains 47 grams. Your H. pylori will be VERY pleased if you drink one of those, especially if you use it to wash down the white flour bun on your hamburger.

I do think it's important to mention that the study described above used isolated fructose. It's not clear that other sources of fructose would behave the same. For example, the presence of glucose enhances fructose absorption. Fruit, table sugar and high-fructose corn syrup all contain glucose. It's also not clear what the effect would be of eating fructose with a meal rather than in isolation. None of this has been studied to my knowledge, so we're left extrapolating from studies that used pure fructose.

Now let's connect the dots. Excessive fructose, certain types of fiber, and wheat cause bacterial overgrowth and H2 production (if you believe the fructose-H2 connection). Elevated H2 causes overgrowth of H. pylori and possibly other pathogenic bacteria in the body. H. pylori lowers stomach acid, causing further overgrowth of bacteria in the small intestine. This causes inflammation and increases the risk for digestive cancers.

Decreased stomach acid also causes malabsorption of protein, B12, iron and perhaps other nutrients. It allows undigested protein to travel into the small intestine. This could potentially be very important. For example, many people are allergic to the casein in milk. It's one of the two most common alleriges, along with gluten. Both casein and gluten are proteins. A normally functioning stomach at the proper pH should completely digest casein. You can't be allergic to casein if there's none around. I don't know if the same applies to gluten.

Robust digestion may explain why many healthy non-industrial groups do very well eating dairy, sometimes to the exclusion of nearly everything else, yet many people in modern societies do better without dairy protein (butter is typically well tolerated). This phenomenon could also go a long way toward explaining the fact that allergies are becoming more and more common in industrial nations as we consume more sugar.

Thanks to Peter and Matt Stone for some of the ideas I incorporated into this post. Thanks to pbo31 for the CC photo.

Exercise and Bodyfat

I'm a firm believer that exercise is part of a healthy pattern of living. Hunter-gatherers had a word for exercise: "life". Getting outdoors and moving is one of the few things that differentiate modern humans from lab rats.

That being said, there are some common misconceptions about the activity patterns of hunter-gatherers and healthy non-industrial groups. They aren't (usually) couch potatoes, but they don't necessarily exercise a lot either. They range from very active to positively lazy, depending on the culture, the season and the gender concerned. Yet overweight is rare in all of them.

Consider the Kitavans. According to Dr. Staffan Lindeberg, the only overweight person on the whole island is someone who left for several years to live in a city. An average Kitavan man has a BMI of 20, which is very lean. Women have an average BMI of 18! A BMI of 25 is considered overweight and 30 is obese. The average Swede has a BMI of 25, the average American, 28. Kitavans have the activity level of a moderately active Swede, nothing more. They do the minimum amount of work required to grow their starchy tubers and fruit, and catch fish, all of which are abundant year-round. They are not restricted in calories.

Then there are the Tokelauans. Between 1968 and 1982, residents of the Pacific atolls of Tokelau gained roughly 11 pounds (5 kg) on average. This corresponded with a shift in diet from traditional Polynesian foods to a partial reliance on white flour, sugar and other processed foods. During this period, men exercised progressively less due to the introduction of the outboard motor, but the activity level of women stayed roughly the same. Both genders gained weight. Calorie intake didn't trend in any particular direction during the same time period.

Tokelauans who migrated to New Zealand saw a particularly large weight gain, gaining 22 pounds (10 kg) over the same time period. Their diet became even more Westernized than their relatives who remained on Tokelau. The authors of the Tokelau Island Migrant study felt that "most of the migrants expend greater energy in their work than is currently the case in Tokelau."

The "paradoxes" keep rolling in. In this recent study, investigators compared the energy expenditure of Nigerian and African-American women, using direct measurement (respiratory gas exchange and doubly labeled water) rather than questionnaires and observation. Here's what they found:

Mean body mass index (in kg/m(2)) was 23 among the Nigerians and 31 among the African Americans; the prevalences of obesity were 7% and 50%, respectively. After adjustment for body size, no differences in mean activity energy expenditure or physical activity level were observed between the 2 cohorts.

Are you bored yet? Here's another one, just in case your eyes are still open. I'll quote from Stefansson's Cancer, Disease of Civilization, referring to traditional point Barrow Inuit women in wintertime. The section in quotes comes from the anthropologist Dr. John Murdoch:

"They are large eaters, some of them, especially the women, eating all the time..." ...during the winter the Barrow women stirred around very little, did little heavy work, and yet "inclined more to be sparse than corpulent"

One last example. Americans have gained weight continually over the last 40 years, despite increasing leisure-time exercise and an increased energy expenditure. Our calorie intake has increased over the same time period, and the quality of our diet has deteriorated.

I think it's clear that the relationship between exercise and weight is not very tight. In my opinion, diet has a much larger influence on weight than exercise. Doing low-intensity "cardio" on a treadmill is almost totally ineffective for weight loss.

So can exercise help a person reach or maintain a healthy weight? Absolutely, but the type of exercise is critical. Exercise plugs into some of the same metabolic pathways as a healthy diet, normalizing hormone levels and increasing stress resitance. All you have to do is pop over to Chris's Conditioning Research to see a number of studies that compared chronic cardio (as Mark Sisson would say) to high-intensity, intermittent training (HIIT). HIIT is the winner every time by virtually every measure. Even though a person burns fewer calories sprinting on and off for five minutes than she does running for 30, she will still lose more fat and gain more muscle sprinting because of the metabolic shift that type of training produces.

In one study Chris posted, investigators compared the effect of two different exercise styles on fat loss and metabolic parameters. One group was assigned to low-intensity steady-state exercise, while the other was assigned to short 8-second sprints (called HIIE in this study). Here's what they found after 15 weeks:

Both exercise groups demonstrated a significant improvement (P less than 0.05) in cardiovascular fitness. However, only the HIIE group had a significant reduction in total body mass (TBM), fat mass (FM), trunk fat and fasting plasma insulin levels.

I think exercise is part of the fat loss / maintenance toolkit, along with intermittent fasting. But nothing beats a good diet.