Question: Is there anything to those so-called "blood type diets?"

The answer is absolutely... maybe.

I wish I could give you the flip answer I used to give a few years ago when asked about this: "Diets based on your blood type are nutritional astrology!" But the truth is I'm not as sure as I once was that it's all hokum, though the way many people interpret it is pretty much bullshit.

Here's the theory in a nutshell: There's a chemical reaction between your blood and the foods you eat caused by a diverse group of proteins in foods called lectins. According to Peter D'Adamo, author of Eat Right for your Type, when you eat a food containing lectins that are incompatible with your blood type, the lectins target an organ and begin to agglutinate blood cells. It's not life threatening, but it can make you feel crummy.

According to Michael Lam, MD, MPH, 95% of the lectins you absorb from your diet are sloughed off by the body, but about 5% aren't. Those that aren't sloughed off make it into your bloodstream and cause various reactions in different organs.

If you've never heard of any of this stuff, here's the Readers Digest version:

• Type O is a high-protein meat-eating type like Charles Poliquin.
• Type A is your typical tofu-eating vegetarian that gets sand kicked in his face by, well, guys like Charles Poliquin.
• B and AB are "mixed types" that can eat most anything.

Of course it's more complicated than that, but that's the basics. There has been some research – notably by Laura Power, Ph.D. – on the influence of blood type on diet, and it does seem that blood type may be one contributing factor in determining which foods work best for any given person. But there are more than a few caveats.

First, there are a lot more than the four blood types you read about in the popular blood type diet books. In fact, there are about 20 different subtypes just among people with type A blood alone! These subtypes may have important differences, and may not all react to food in the same way.

The second problem is that blood type is one factor of many. For example, I've seen more than a few type A's who feel like crap on a vegetarian diet. And though your "type" may thrive on dairy, you might be lactose intolerant, making the whole point moot.

Third of all, people who really use blood type as a serious diagnostic and nutritional planning tool do a lot more than figure out your type. Naturopathic physician Dekker Weiss, NMD, a big blood type supporter, told me that he does all kinds of ancillary tests besides blood tests to determine how to personalize the diet for best results.

My personal opinion is that just using the four blood types as a basis for an entire diet is pretty flimsy, and I think that even most blood type supporters would agree with me. Even D'Adamo, who popularized the whole shebang, offers an intensive seminar for health professionals to show you how to use it properly.

And Laura Power, who did the research I mentioned, has recently built on the blood type data to create what she calls eight "Biotypes."

Meanwhile, I try my own personal "What's your sign?" party trick with blood types all the time. If someone's a big meat eater and tells you he feels great on the stuff, there's a good chance he's a type O. Works every time.

Question: Is rhodiola worth using or is it all hype?

It's pretty good stuff, actually.

Rhodiola rosea is a plant that grows in really cold climates, like the Alps and Iceland. It's known as an "adaptagenic," which means it can bring you up if you're down and down if you're up, much like the thermostat does with the temperature in your house. It's used for improving mood, reducing stress, and fighting fatigue.

And the research on it is pretty good.

A 2002 review published by the prestigious American Botanical Council concluded that numerous studies of rhodiola show that it helps prevent fatigue and reduce stress. According to Dr. Andrew Weil, it also enhances immune function and increases sexual energy.

A double-blind, placebo-controlled, randomized study investigated the effect of rhodiola on physical capacity, muscle strength, speed of limb movement, reaction time, and attention in healthy volunteers. The results documented that rhodiola can improve endurance exercise capacity. (Int. J Sport Nutr Exerc Metab; 14(3): 298-307, 2004).

Another study tested the effect of rhodiola in 40 foreign students during a stressful exam period. The most significant improvement was seen in physical fitness, mental fatigue, and neuromotor tests. There was also a significant improvement in general well-being in the rhodiola group.

So no, it's not hype at all. And best of all, you can try it pretty safely since it has virtually no side effects and there are currently no contraindications with prescription meds. The staid Physicians Desk Reference for Herbal Medicines says, "Rhodiola may be helpful in relieving mental and physical fatigue and improving endurance exercise performance and general well-being."

Recommended dose is 50-200mg per day. Just make sure to buy it from a reputable source, not from some clown in an infomercial.

Question: In your book, The 150 Most Effective Ways to Boost Your Energy, you mentioned Lo Han, some type of sweetener. What's the scoop on this stuff? I've never heard of it!

Lo Han (not to be confused with the supremely self-involved actress) is the common name for a sweetener extracted from the Luo Han Guo plant found in the mountains of southern China. It's also known as Luo Han Guo and Luo Han Kuo.

Lo Han has a vanishingly low glycemic impact, is way sweeter than sugar – about 250 times sweeter – and can be used with both hot and cold foods, so you can cook and bake with it or add it to coffee or tea.

If you want to try it, Jarrow Formulas makes a nice product called Lo Han Sweet. It has about two calories per serving (about half a teaspoon).

Question: Are there any foods that act as aphrodisiacs?

Oh dude, do I wish.

Question: Are there specific foods, or specific patterns of eating, that cause more fat to accumulate in the abdominal area? On a related note, does beer really cause a beer belly by preferentially storing fat there?

Are there foods that cause fat to accumulate on the belly? Yes: foods with too many calories and too much sugar.

Does that clear it up for you?

Okay, seriously, it's a good question and here's the answer: When you drive insulin levels up high as you do with high-sugar foods or high intakes of processed "CC's" (crappy carbs – it's a technical term), you increase the chances of insulin resistance. Insulin resistance nearly always goes hand-in-hand with a big fat belly.

In fact, the "low-tech" test for insulin resistance is this: If you walk towards a wall, does your belly hit the wall before you do? A guy with a waist over 40 inches and a woman with a waist over 35 inches nearly always have insulin resistance. You bring insulin resistance down with a low-carb diet.

Now obviously, it's not just sugar and carbs that make you fat, but they do send insulin – also known as the "fat storage hormone" – into overdrive.

You could eat 10,000 calories a day from coconut oil and you'd be fat as a horse, even though there aren't any any carbs in it. And you could conceivably be fat as a tub and carry most of that fat on your back or your thighs, hips, and butt. Still, if I were trying to avoid a spare tire around the middle, the first place I'd look to cut would be sugar and processed carbs.

As for beer bellies: Although a lot of beers don't have a ton of carbs, the belief is that beer may contain estrogenic compounds that cause the fat to accumulate on your body in a pattern that makes you look like Rosie O'Donnell – or Rosie Greer.

In any case, if you're putting away a six-pack every night, just from a calorie point of view it's going to create fat storage. Remember, they didn't start calling it "beer belly" because the term "steak belly" was already taken.