Can you trust online health advice?

“10 ways to boost your metabolism.” “9 foods that lift your mood.” ”15 supplements to boost your immune system.” People love lists. So do websites eager to grab eyeballs. Only one problem: Much of the advice isn’t based on solid science. Here are 8 examples.

1. Can antioxidant supplements prevent skin cancer or wrinkles?

“Your skin needs the right balance of nutrients,” says WebMD. Much of its advice focuses on antioxidants:

Vitamin A. “Since it’s an antioxidant, it may give your skin some protection against sunburn (although not as much as wearing sunscreen).”

Vitamin C. It’s a “powerful antioxidant, protecting you from free radicals and possibly lowering your chance of skin cancer.”

Vitamin E. “This antioxidant and anti-inflammatory can also absorb the energy from UV light, which damages skin and leads to wrinkles, sagging, and skin cancer.”

Zinc. It “acts like an antioxidant” and “may protect skin from UV damage.”

Selenium. It “helps certain antioxidants protect your skin from UV rays. Selenium deficiency has been linked with a greater chance of skin cancer.”

But the best evidence doesn’t back up those claims. Selenium supplements (200 micrograms a day), for example, raised the risk of a new (non-melanoma) skin cancer in a large clinical trial in 1,312 people with an earlier cancer.

Then there’s the SU.VI.MAX trial, in which French researchers randomly assigned some 13,000 people to take a placebo or a daily supplement with vitamin C (120 mg), vitamin E (30 mg), selenium (100 mcg), zinc (20 mg), and beta-carotene (6 mg), which the body converts to vitamin A. After 7½ years, the antioxidant takers had no lower risk of skin cancer. In fact, there was a hint that women had a higher risk, though that finding needs followup.

Bottom line: Want to prevent skin cancer and wrinkles? Don’t smoke and use sunscreen, a hat, and shade to avoid UV rays.

2. Do omega-3s, vitamin C, or other supplements curb brain fog?

Brain fog “refers to a group of symptoms such as trouble with memory, inability to concentrate, difficulty processing information, fatigue, and scattered thoughts,” says Healthline.com. Its advice to treat the poorly defined problem:

Vitamin D. It “may help improve memory, concentration, and mood in some people, which may help alleviate brain fog.” Yet the website only cites inconclusive studies on depression, “negative emotions,” and “a small study” on memory. “More research is needed,” says Healthline. Indeed.

Omega-3 fats. They can “improve certain symptoms of brain fog, including difficulties with attention and memory.”

Really? Healthline cites no studies that tested omega-3s on people with brain fog. Instead, it says, omega-3s may “improve depressive symptoms and boost mood, which may help reduce symptoms of brain fog.”

But in a rigorous review of 33 trials, omega-3s had no clinically meaningful benefit for treating depression. Nor did omega-3s help prevent depression, anxiety, or memory loss. 

Magnesium. Trials showing that it curbs depression? Scanty. Brain fog? Zip.

Vitamin C. Unless you’re deficient, there isn’t much evidence that it helps.

B Complex. “Low or deficient levels of certain B vitamins can lead to symptoms of brain fog,” says Healthline. That’s true for a vitamin B-12 deficiency, but the evidence for other B vitamins is less clear.

L-theanine. “A recent study in 69 adults ages 50–69 found that a single dose of 100.6 mg of L-theanine improved reaction time and working memory.”

Healthline forgot to mention that taking L-theanine every day for 12 weeks had no effect...on 20+ measures of attention or memory. Oops.

Bottom Line: If you’re over 50 or a vegan, get 2.4 mcg a day of B-12 from a supplement or food with added B-12.

3. Do foods like citrus fruit or onions boost immunity?

“For better immunity, here are some of the best foods to put on your plate,” says Everydayhealth.com. Among them:

Seafood. “The omega-3 fatty acids found in some types of fish—such as salmon, sardines, herring, and mackerel—enhance the functioning of immune cells,” says a dietitian quoted by Everydayhealth.com.

But even the small, uncontrolled study the website cites calls for other studies “to determine whether the observed changes in immune function translate into clinical benefits.” Got that right.

Healthy proteins. They contain zinc, and some immune cells “can’t function without zinc.” True, but there’s no good evidence that zinc-rich foods ward off colds or the flu.

Dark chocolate. It has magnesium, “which may strengthen antibodies and help prevent disease.” Any good evidence that eating more magnesium—or chocolate—fends off infections? Nope.

Citrus fruit. Can vitamin C prevent colds? No, except maybe at huge doses (250 to 1,000 mg a day) after intense exercise, like an ultra-marathon.

Garlic & onions. “When garlic is crushed or chopped, it produces allicin, which previous research has highlighted for its antiviral and antibacterial properties.” But claims that garlic fights colds “appear to rely largely on poor quality evidence,” says a review cited by Everydayhealth.com.

As for onions, they contain quercetin, which inhibits flu virus...in test tubes, says another cited study.

The article goes on to say that you’re better off with water than juice, adding that “there’s no proof that OJ prevents or shortens illness.” Ditto for all Everydayhealth.com’s “immune system boosters.”

Bottom Line: Many nutrients play a role in immunity, but eating more of them doesn’t prevent infectious illness.

4. Are certain foods natural appetite suppressants?

“These natural appetite suppressant foods are filled with nutrients,” explains Shape.com. The list includes:

Almonds. “Almonds have been shown to increase feelings of fullness in people and help with weight management, according to a 2006 study.”

In fact, that industry-funded study didn’t measure fullness. But a 2017 industry-funded study by one of the same researchers did. And its results “do not support a unique satiety effect of almonds,” concluded the authors.

Cayenne pepper. “Just half a teaspoon of cayenne pepper can boost metabolism and cause the body to burn an extra 10 calories on its own, according to research published in the journal Physiology & Behavior.” 

People in the study (it was partly industry-funded) who got the cayenne did burn an extra 10 calories...over 4½ hours. That’s about what you’d get in one tablespoon of whole milk.

Eggs. “Studies have shown that eating an egg or two for breakfast can help you feel more full over 24 hours than if they [sic] eat a bagel with the same amount of calories.” “In the same study, those who ate eggs ingested an average of 330 fewer calories over the course of a day than the bagel-eaters.”

The people in the industry-funded study did report feeling more full and ate 265 (not 330) fewer calories on the egg day. And, in another industry-funded study, when the researchers told people to eat 1,000 fewer calories a day for two months, those assigned to eat egg breakfasts did lose more weight (6 pounds) than those told to eat a bagel breakfast (3½ pounds). But breakfast had no impact on weight loss when people were not told to cut calories.

And in yet another industry-funded study, eating egg breakfasts instead of cereal breakfasts for six months had no impact on weight loss when people were told to cut calories.

Bottom Line: Most claims about “appetite suppressant” foods are backed by inconclusive research.

5. Can a healthy diet prevent cervical cancer?

“Diet and nutrition play a role in the development of cervical cancer,” says MedicalNewsToday.com. Really?

“Up to 99.7% of cervical cancer cases result from infection with the human papillomavirus (HPV),” says the website. “There are three HPV vaccines that protect against some strains of HPV known to cause cervical cancer.” So far, so good.

The problem: Medical News Today then says that “Adequate nutrition helps to optimize the immune system, which, in turn, eliminates HPV and helps the body respond against cancer tumors.”

So a healthy diet enables the immune system to eliminate HPV...and helps fight tumors? Surely, no one would say that without strong evidence. Yet some of the studies cited by Medical News Today looked only:

• at cancers other than cervical cancer
• at mostly the impact of folate (a B vitamin) on cervical cancer cells in test tubes
• at whether women with a genetic variant for the vitamin D receptor have a higher risk of cervical cancer.

“Adopting a dietary pattern similar to the Mediterranean diet reduces inflammation and cervical cancer risk,” says the website. Then why did the study it cites find no lower odds of precancerous cervical lesions in women who ate the most Mediterranean-​like diet?

A Mediterranean diet is heart healthy. But the evidence that it prevents an HPV infection or cervical cancer is skimpy.

Bottom Line: To lower cervical cancer risk, don’t smoke, get the HPV vaccine (typically only if you’re under 27), use a condom to help prevent an HPV infection, and get routine Pap tests to detect precancerous lesions (ask your doctor if you’re over 65). For more, check the websites of the National Cancer Institute, American Cancer Society, or American Institute for Cancer Research.

6. Does dark chocolate protect your heart, skin, or brain?

Among Healthline’s “7 proven health benefits of dark chocolate”:

Very nutritious. “A 100-gram bar of dark chocolate with 70–85% cocoa contains: 11 grams of fiber, 67% of the DV for iron, 58% of the DV for magnesium, 89% of the DV for copper, 98% of the DV for manganese.”

Yes, but “100 grams (3.5 ounces) is a fairly large amount,” concedes Healthline, so “these nutrients also come with 600 calories.”

A serving is only 30 grams. So...why even mention a 100-gram serving?

Blood flow and blood pressure. “The effects are usually mild.” And “one study in people with high blood pressure showed no effect, so take this with a grain of salt.” So...not a “health benefit”?

Raises HDL and protects LDL from oxidation. But in the study cited by Healthline, HDL didn’t increase—and oxidized LDL didn’t decrease—more in people who drank cocoa with polyphenols than in those who drank placebo cocoa.

May reduce heart disease risk. After citing studies where dark chocolate or cocoa “lowered the risk” of outcomes like heart disease, Healthline adds that “these four studies are observational, so it’s unclear exactly if it was the chocolate that reduced the risk.” So...not “proven”?

May protect your skin from the sun. “In one study of 30 people, the MED more than doubled after consuming dark chocolate high in flavanols for 12 weeks.” (MED is the minimum amount of UVB rays required to make skin red.)

“If you’re planning a beach vacation, consider enjoying some extra dark chocolate in the prior weeks and months. But check with your doctor or dermatologist before forgoing your normal skin care routine.”

So...you can skip the sunscreen?

Could improve brain function. “One study of healthy volunteers showed that eating high flavanol cocoa for 5 days improved blood flow to the brain.” But blood flow may not translate into better memory or other measures of “brain function.”

Bottom Line: Dark or not, chocolate isn’t a health food.

7. Do some foods boost your metabolism?

Metabolism is “your body’s system for turning what you eat and drink into energy,” says WebMD.

But what follows is a list of foods that “support a healthy metabolism” or “keep you full” or “won’t cause major spikes in your blood sugar (too much sugar in your blood gets stored as fat).”

(Note to WebMD: If you eat more calories than you burn, they get stored as fat, whether your blood sugar “spikes” or not. Pure fructose, for example, barely raises blood sugar, but its calories still count.)

So which foods “support” your metabolism, according to WebMD?

Iodine-rich foods. “The thyroid gland plays a key role in helping your metabolism burn calories and control your appetite. To do its job, your thyroid needs healthy levels of iodine.”

True enough. But unless you’re deficient—most Americans aren’t—getting more iodine won’t boost your metabolism.

Water. Drinking more than usual before meals may “help you take in fewer calories.” But does it “boost calorie burning if you’re obese” or “help your body burn fat,” as WebMD claims? Nope. (Water only helps your body burn fat if it “helps you take in fewer calories.”)

Ginger. “One study found that drinking a hot ginger drink with breakfast lowered feelings of hunger and had a strong thermogenic (calorie-burning) effect.”

Strong? The thermogenic effect was barely significant. And researchers never followed up on this 2012 pilot study on just 10 men.

Legumes. Beans are indeed rich in fiber. But no, the fiber doesn’t make “your metabolism work harder to digest them.”

Avoiding sugar-sweetened drinks. Yes, they have “lots of calories.” But there’s no good evidence that they “negatively impact your metabolism beyond the ‘calories in, calories out’ rule.”

Bottom Line: Want to boost your metabolism? Move more.

8. Can probiotics, protein powder, or other supplements make you more energetic?

“Dietary supplements can be a great way to get sufficient amounts of essential vitamins and minerals in order to really start to see a difference in your energy as you work through the day,” says the “Eat This, Not That!” website. The list includes:

Probiotics. “If your gut health is out of whack, your energy levels may take a dive.”

If you were expecting good evidence that probiotics make people feel more energetic, it’s not here. Even the evidence that most probiotics improve gut health is weak.

Vitamin B-12. It “helps our cells convert the food we eat into energy, and when we are deficient we tend to feel weak, tired, and lightheaded,” says one dietitian quoted by EatThis.

Another notes that a B-12 deficiency can cause anemia. “Here’s the kicker,” says EatThis. “This form of anemia causes low energy and fatigue.”

News flash: Any anemia causes low energy and fatigue, because your red blood cells aren’t carrying enough oxygen to the rest of your body. That’s largely why “we tend to feel weak, tired, and lightheaded.”

Ashwagandha. “Ashwagandha naturally reduces cortisol levels, especially those elevated due to ongoing and uncontrolled stress. Improving mental fatigue and stress can lead to improvements in overall energy.”

Ah, so there’s no good evidence that ashwagandha makes people feel more energetic? As it turns out, the evidence that it reduces stress isn’t solid, either.

Protein powder. A protein powder one dietitian recommends is “rich in vitamin B, and we know how essential that is to maintain our energy,” says EatThis.

Here’s what we really know: There are eight B vitamins, not one. And while some help release energy from food, that’s not the same as making you feel energetic.

Bottom Line: Tired? Get enough food, sleep, and exercise.