The Benefits of Wakame Seaweed Salad on Blood Pressure

I used to think of seaweed as just a beneficial whole-food source of minerals like iodine, for which it is the most concentrated dietary source. Indeed, just a daily half-teaspoon of mild seaweeds, like arame or dulse, or two sheets of nori should net you all the iodine you need for the day. But, the intake of seaweeds is advised not only as a whole-food source of iodine, but also, evidently, “for the prevention of lifestyle-related diseases, including cancer, cardiovascular and cerebrovascular disease….” Based on what?

As I discuss in my video Wakame Seaweed Salad May Lower Blood Pressure, the reasoning is that the Japanese live long and eat seaweed, so there is speculation that seaweed might have “influence on life expectancy,” based on suggestive reports. But when we see long lists of the supposed benefits a particular food is purported to have, such as “compounds found in [seaweed] have various biological activities including anticoagulant, anti-viral, antioxidant, anti-allergic, anti-cancer, anti-inflammatory, anti-obesity, and neuroprotective properties,” we need to know if they are based on clinical data, meaning studies with actual people, or so-called preclinical data, that is, from test tubes and lab animals. I mean, what are we supposed to do with a study talking about the effects of “seaweed-restructured pork diets” on rats? Those researchers tried to use seaweed, as well as other ingredients, to “improv[e] the ‘image’ of meat product.” Researchers also tried to add grape seeds to meat, they tried flaxseeds, they tried walnuts, they tried purple rice, and they even tried “thong-weed.”

When you look at epidemiological studies, where you compare the diets and disease rates within a population, you see that Japanese pre-schoolers who eat seaweed tend to have lower blood pressures, suggesting “seaweed might have beneficial effects on blood pressure among children.” That could make sense given all the minerals and fiber in seaweed, but cause and effect can’t be proven with this kind of study. Perhaps other components of the diet that went along with seaweed eating that made the difference.

It’s even harder to do these kinds of studies on adults, since so many people are on high blood pressure medications. University of Tokyo researchers took an innovative approach by comparing the diets of people on different intensities of medication: low-dose of a single blood pressure drug, high-dose of a single drug, and multiple drugs. And, although they all had artificially normalized blood pressure “as a result of effective medication,” those who ate the most fruits and sea vegetables tended to be the ones on the lower dose of a single drug, supporting a dietary role for seaweed. An interesting finding, but why not just put it to the test?

A double-blind, crossover trial found that seaweed fiber lowered blood pressure, apparently by pulling sodium out of the system. Real seaweed couldn’t be used in the study, because the subjects wouldn’t be able to be fooled with a placebo, but why not just put whole powdered seaweed into pills? That was finally attempted ten years later. Compared to doing nothing, subjects receiving a daily dose of dried wakame powder in capsules had beautiful drops in blood pressure. The researchers, however, desalinized the seaweed, taking out about two-thirds of the sodium naturally found in it. So, we still don’t know if eating seaweed salad is actually going to help with blood pressure. What we need is a randomized, controlled trial with plain, straight seaweed. No one had ever done that research, until…they did!

Six grams of wakame, with all of its natural sodium, led to a significant drop in blood pressure, especially in those who started out with high pressure. The subjects experienced only minor side effects and ones that could be expected with increasing fiber intake. A nice thing about whole-food, plant-based interventions is that we sometimes get good side effects, such as the resolution of gastritis (stomach inflammation) some subject had been having, as well as the disappearance of chronic headaches. 


What other foods might help with high blood pressure? See:

For more on preventing and treating hypertension, one of our leading killers, see:

Want more on seaweed and iodine? Check out:

My video Salt of the Earth: Sodium and Plant-Based Diets further addresses the sodium question.

In health,
Michael Greger, M.D.

PS: If you haven’t yet, you can subscribe to my free videos here and watch my live, year-in-review presentations:

Why it’s Better to Drink Green Smoothies With a Straw

A group of women were split into two groups and told to eat as much soup as they wanted, but half were given big spoons and told to eat quickly, while the other half were given small spoons and told to eat slowly. The slow group ended up feeling more satiated—despite eating less food. Prolonged meal duration can allow more time for our body’s own “I’ve-had-enough” signals to develop before too many calories have been consumed. It makes sense. After all, we evolved for millions of years before cooking, when undomesticated fruits and vegetables were much tougher and fibrous. Our body is built to expect us to take our time when eating.

What about when drinking? There weren’t any blenders on the African savannah. In smoothie form, you can drink fruits and vegetables at about two cups a minute—ten times faster than it might take to eat fruits and vegetables in solid form. Liquid calories can be consumed so quickly they can undermine our body’s ability to regulate food intake at healthy levels. It’s not the liquid texture per se, but the high rate of consumption at which liquids are normally consumed. Blend all the smoothies you want, but sip them slowly for a half hour or so rather than gulping them down.

Even when sipped slowly, though, an all-fruit smoothie may not be as filling as eating a whole fruit, so the more greens you can add to your smoothie the better. You can also add ground flax seeds. As you can see in my video, The Downside of Green Smoothies, the thicker the smoothie, the less hungry you are one, two, and even four hours later—and flax seeds make for thick, milkshake-type smoothies. Researchers found that one tablespoon of flax seeds significantly suppresses appetite and calorie intake. You can give someone a meal two hours after the tablespoon of flax seeds, and they eat significantly less—all the while dropping their cholesterol in only one week when eating about a tablespoon of flax seeds each day.

The fat naturally found in flax seeds can also help maximize the absorption of fat-soluble phytonutrients. There’s a threshold for optimal absorption that can be reached with just about three walnuts worth of fat. If we’re trying to reduce added fats, a green smoothie with some nuts, seeds, or avocado can enable us to take full advantage of the healthiest foods on the planet—dark green, leafy vegetables.

Smoothies also allow us to eat parts of fruits and vegetables we might not otherwise. If, instead of the lemon juice called for in Mayo Clinic’s basic green smoothie recipe (shown in the video), you used a little wedge of lemon, you might get some seeds and peel, which in vitro at least, appear to suppress both breast cancer and colon cancer cell growth.

Clinical studies on smoothies show what you’d expect to see from eating great foods like greens and berries—enhanced athletic performance and recovery, boosting the antioxidant power of your bloodstream, and potentially improving arterial function in both the short- and long-term. Kiwifruit smoothies protect against DNA damage, and strawberry smoothies protect against inflammation. Of course, presumably, so would just eating greens, kiwis, and berries intact.

There’s been some concern expressed that drinking green smoothies would bypass the nitrate-reducing bacteria in the mouth, but our body’s way too smart for that; it pumps nitrate back into our salivary glands. Even if we deposited greens directly into our stomach with a tube, we’d still produce the nitric oxide so important for artery health.

Concerns have been raised that the oxalic acid in vegetables might increase kidney stone risk, but, as research shows, the opposite might be the case. (See How to Treat Kidney Stones with Diet.) So are there any downsides of smoothie consumption?

Whether with lemon juice or a lemon wedge, smoothies can be sour. Any time you’re eating or drinking something sour, you have to be careful about eroding the enamel on your teeth. Researchers found that if you soak teeth in a smoothie for an hour, significant enamel is eroded away. But who soaks their teeth in a smoothie for an hour?

What if you instead study the effects of smoothies in situ (meaning in position), as opposed to in vitro (meaning in glass)? If you make people wear slabs of enamel in their mouths while they drink a smoothie to replicate a typical tooth exposure, researchers find almost as much erosion as drinking Diet Coke. So, it’s recommended that smoothies be consumed through a straw, similar to the advice given for other acidic beverages like soda or hibiscus tea. Drinking juice through a straw has less of an acidic effect than swishing it around in your mouth, so avoid swishing around mouthfuls of smoothie in your mouth. You also want to wait at least an hour before brushing so as not to brush your enamel in a softened state; rinsing your mouth with water after drinking smoothies can help rinse away some of the acids to protect your teeth.

One final caveat for smoothies: When I advocate green smoothies to boost fruit and vegetable consumption, I’m talking about whole food smoothies, not those made from juice or with added sugars—or human organs. Some women choose to consume their afterbirth. Though described as “replenishing and delicious,” the problem with eating one’s placenta is that one of the functions of the placenta is to filter out toxins, so it may be contaminated with heavy metals, as well as pose a food poisoning risk if consumed raw, like in a smoothie. Green smoothies are great, but I’d be cautious about drinking certain types of red smoothies.


I have several videos on smoothies: Are Green Smoothies Good for You?, Are Green Smoothies Bad for You?, Green Smoothies: What Does the Science Say?, Liquid Calories: Do Smoothies Lead to Weight Gain?, and A Better Breakfast.

Was the concern about dental erosion new to you? See more in Plant-Based Diets: Oral Health, Plant-Based Diets: Dental Health, and Protecting Teeth from Hibiscus Tea.

What’s with that nitrate thing? See Don’t Use Antiseptic Mouthwash. So, What’s the Best Mouthwash? Watch to find out.

For more on fat-soluble nutrient absorption, check out an ancient video of mine, Forego Fat-Free Dressings?. And for more on oxalates and kidney stones, there’s How to Prevent Kidney Stones With Diet and How to Treat Kidney Stones with Diet.

In health,

Michael Greger, M.D.

PS: If you haven’t yet, you can subscribe to my free videos here and watch my live, year-in-review presentations:

Sip Smoothies Slowly

A famous study in 2000 compared the impact of soda versus jelly beans. Researchers had people add 28 extra spoonfuls of sugar to their daily diet in the form of jelly beans or soda. Then, they measured how many calories participants ate over the rest of the day to see if their bodies would compensate for all that extra sugar. For the jelly bean group, their bodies registered all the extra calories from the handfuls of jelly beans and they ended up eating less of everything else throughout the day. So, they ate pretty much the same number of calories before and after adding the jelly beans to their diet. But, for the soda group, despite all the added calories from the cans of pop they were drinking every day, they kept eating about the same amount. No wonder they gained weight after a month of drinking soda. Their bodies didn’t seem to recognize the extra calories when they were in liquid form and therefore didn’t compensate by reducing their appetite for the rest of the day.

What if we drink a smoothie for breakfast instead of eating a solid meal? Will our body think we skipped breakfast and make us so ravenous at lunch we’d eat more than we normally would and end up gaining weight? To answer this, we first have to determine if this solid versus liquid calorie effect is real. Soda and jelly beans don’t just differ by physical form; they have different ingredients. That’s a problem with a lot of these kinds of studies: They use dissimilar foods.

Take, for example, the study comparing liquid to solid breakfasts in my video Liquid Calories: Do Smoothies Lead to Weight Gain?. Researchers gave participants breakfasts of either fruit juices and skim milk or oatmeal with blueberries and apples. Not so surprisingly, study subjects were less hungry after the oatmeal. But, that may not be a solid versus liquid effect, as the breakfasts were comprised of completely different foods.

To test for a solid versus liquid effect, you’d have to use the exact same foods in two different forms. Finally, a study did just that. Researchers looked at what happens if you have a fruit salad with raw apples, apricots, and bananas with three cups of water to drink versus blending the fruit with two of the cups of water to make a smoothie and then just drinking the third cup of water. It’s the identical meal—one in solid form and one in smoothie form. What happened? People felt significantly less full after the smoothie, although it was the same amount of food and fiber. In smoothie form, it didn’t fill people up as much as eating fruit au natural.

Originally, we thought it was due to the lack of chewing. The act of chewing itself may be an I’ve-eaten-enough signal that you don’t get just by drinking. Researchers had people chew either 10 or 35 times per mouthful and eat pasta until they felt comfortably full. Those forced to chew 35 times per bite ended up eating about a third of a cup less pasta than those who only chewed 10 times per bite. So there we have it: We had the proof of solid versus liquid effect and the mechanism. But, as so often happens in science, just when we have everything neatly wrapped up with a bow, a paradox arises.

In this case, the great soup paradox.

Pureed, blended soup—essentially a hot, green smoothie of blended vegetables—is more satiating than the same veggies in solid form. The same meal in liquid form was more filling than in solid form. So, it can’t be the chewing that has the satiating effect. In fact, there doesn’t appear to be a solid versus liquid effect at all since cold smoothies appear to be less filling, but hot smoothies appear to be more filling. They are so filling that when people have soup as a first course, they eat so much less of the main course, that they eat fewer calories overall, even when you add in the soup calories.

How can we explain this paradox? Maybe pureed fruit is less filling than solid, but pureed vegetables are more filling? To test this, Purdue University researchers used apple soup. They mixed about a cup of apple juice with two cups of applesauce, liquefied it in a blender, and heated it up. If you have people eat three actual apples, they started out pretty hungry, but, within 15 minutes of eating the apples, they were hardly hungry at all. Drinking three cups of apple juice didn’t cut hunger much, but what about the apple soup, which was pretty much just hot apple juice with applesauce mixed in? The apple soup cut hunger almost as much as the whole apples, even more than an hour later. It even beat out whole apples for decreasing overall calorie intake for the day.

What’s so special about soup? What does eating soup have in common with prolonged chewing that differentiates it from smoothie drinking? Time. It took about twice as long to chew 35 times. And think about how long it takes to eat a bowl of soup compared to drinking a smoothie. Eating slower reduces calorie intake.

Alternatively, maybe we just imagine soup to be filling, so it’s like a placebo effect. Feelings like hunger and fullness are subjective. People tend to report hunger more in accordance with how many calories they think something has rather than the actual caloric content. If you study people with no short-term memory, like the character in the movie Memento who couldn’t remember what happened more than a minute ago, they can overdose on food because they forgot they just ate, which shows what poor judges we are of our own hunger. It’s not just subjective effects, either. In a famous study called Mind Over Milkshakes, people were offered two different milkshakes, one described as indulgent, “decadence you deserve,” and the other a sensible, “guilt-free satisfaction.” People have different hormonal responses to them even though they were being fooled and given the exact same milkshake.

Finally, maybe it was just because the soup was hot, and warmer foods may be more satiating? How do we figure out if the solution to the soup mystery was time, thought, or temperature? If only the study we discussed earlier that had subjects eat either a fruit salad with three cups of water or drink the same exact foods in smoothie form had a third group—a liquid eating group, too. Well, it did!

Researchers also offered the fruit smoothie in a bowl to be eaten cold with a spoon. (Very un-soup-like.) So, if it were thought or temperature, the fullness rating would be down by the liquid drinking. However, if it was just the slowed eating rate that made soup as filling as solid food, then the fullness rating would be up closer to the solid eating rating—and it was exactly as high. The only real reason smoothies aren’t as filling is because we gulp them down, but if we sip them slowly over time, they can be just as filling as if we ate the fruits and veggies solid.

Wow, that study thought of everything. You don’t know the half of it! They also wanted to see if it would work with high-fat smoothies too. So, what, almond butter or walnuts? No, they used a liquefied fat smoothie of steamed pork belly.

I guess maybe  sometimes smoothies can suppress your appetite 🙂

I have a whole series of videos on smoothies: Are Green Smoothies Good for You?, Are Green Smoothies Bad for You?, Green Smoothies: What Does the Science Say?, and The Downside of Green Smoothies.

For videos on weight gain, see Do Fruit & Nut Bars Cause Weight Gain?, Does Chocolate Cause Weight Gain?, Nuts and Obesity: The Weight of Evidence, and How Diet Soda Can Make Us Gain Weight. 

For weight loss, check out How Much Exercise to Sustain Weight Loss, Brown Fat: Losing Weight Through Thermogenesis, Boosting Brown Fat Through Diet, Eating More to Weigh Less, and Can Morbid Obesity Be Reversed Through Diet?

In health,

Michael Greger, M.D.

PS: If you haven’t yet, you can subscribe to my free videos here and watch my live, year-in-review presentations: