How Nutritious Is That Fish? To Find Out, Ask Its Relatives
By Amy McDermott
Eels and anchovies don't look or act much alike. One is sinuous and shy, the other a bright flash of silver in a school of thousands. Yet the two fish are cousins, both loaded with zinc.
Related fish species—like eels and anchovies—have similar nutritional value, according to a new study in Nature Communications. Two fish can be wildly different on the outside but surprisingly similar on the inside, if they're close on the tree of life.
"There's a shared evolutionary history in the ocean," said food security scientist Bapu Vaitla, who co-led the new study at Harvard's T.H. Chan School of Public Health in Boston, with evolutionary biologist David Collar at Christopher Newport University in Newport News, Virginia.
Turns out, shared evolutionary history is a road map to the patterns of vitamins and minerals fanned through the tissues of fish worldwide. That's a juicy tidbit for researchers studying the links between fish and human health. The specific blend of nutrients in a fish determines how people are nourished when they eat that species.
More than 3 billion people depend on fish for about one-fifth of the animal protein they eat. It's a staple food in dozens of countries, that offers calories, protein, fats and essential micronutrients like iron, zinc, calcium and vitamin A.
Not all fish are the same, though. Cod is much lower in zinc than anchovies, while salmon and trout are fattier than flatfishes, and higher in vitamin D than mackerels. Each species has its characteristic mix of nutrients.
Knowing that mix tells scientists how fish nourish people. It's valuable information, but not cheap or easy work.
Analyzing the nutrient content of one tissue sample costs several hundred to several thousand dollars, said Oceana science adviser Chris Golden, who heads the Harvard research group responsible for the new study. It takes multiple samples, sometimes collected around the world, to build a complete nutrient profile for a species.
Nutrient profiles do exist for hundreds of fish species, but thousands are nutritionally important, Vaitla said. "We couldn't collect samples all over the world, so we needed to predict nutrient content somehow."
The species people eat can say a lot about global health. Oceana / Jon Dee
A Living Mosaic
The oceans are a patchwork of unevenly distributed nutrients. Vaitla and his research partners expected that fish with similar lifestyles, that develop in similar conditions and habitats, would probably be exposed to similar challenges and opportunities, and so be nutritionally alike.
But when the scientists looked across 371 food fish species, they found that body size, preferred habitat and other lifestyle characteristics were not good predictors of nutritional similarity. Instead, genetic relatedness turned out to be key.
"It's not totally unsurprising," said marine ecologist William Cheung of the University of British Columbia, in Vancouver, who was not involved in the new study. Evolutionary relationships click as predictors of nutrition, he said. "Sometimes in science, when someone tells you the answer, you think, ah yes, that's true, that makes sense."
Yet, Cheung said, if he had undertaken the same research, he would've tested lifestyle characteristics first, too. He and Vaitla were both surprised that body size, habitat and other lifestyle characteristics didn't seem to play a role. Vaitla hasn't ruled them out. Repeating the study with more species of fish, he said, could reveal a pattern between lifestyle characteristics and nutrition in the future.
Food for Thought
That related fish are nutritionally similar may not be surprising, but it is useful. Scientists can now predict the vitamin and mineral content of fish species without tissue samples, based instead on their evolutionary relationships.
Predictions could come in especially handy now, as many marine species relocate in response to global change. As they move, they carry their distinct mix of vitamins and minerals with them, exposing fishermen and coastal people to a new mix of nutrients in the fish they eat. When new species move in, they may have different nutritional value from the old staples, exposing communities to risk of malnutrition.
"When we're worried about things like climate change or pollution or overfishing and how its affecting human health, the question amounts to knowing the nutrient landscape out there and how these environmental changes alter that landscape," Vaitla said. "If we're able to know that, we can say things like climate change will impact the availability of iron to this extent, and for these people."
To avoid anticipated risks, communities might curb commercial fishing or set aside marine protected zones, Vaitla said. But first, they need a way to see what's coming. "Evolutionary history," he said, "gives us a shortcut to paint the nutrient landscape out there."
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By Beth Ann Mayer
Since even moderate-intensity workouts offer a slew of benefits, walking is a good choice for people looking to stay healthy.
How to Rock Your Walk<p>Walking isn't just fun and healthy. It's accessible.</p><p>"Walking is cheap," says Dr. John Paul H. Rue, a sports medicine doctor at <a href="https://mdmercy.com/" target="_blank">Mercy Medical Center in Baltimore</a>. "You can do it anywhere at any time; [it] requires little to no special equipment and has many of the same cardio benefits as running or other more intense workouts."</p><p>Want to up your walking game? Try the tips below.</p>
Use Hand Weights<p>Cardio and strength training can go hand-in-hand when you add weights to your walk.</p><p>A <a href="https://journals.lww.com/acsm-msse/Fulltext/2019/03000/Associations_of_Resistance_Exercise_with.14.aspx" target="_blank">2019 study</a> found that weight training is good for your heart, and <a href="https://www.mayoclinicproceedings.org/article/S0025-6196(17)30167-2/abstract" target="_blank">research</a> shows it reduces the risk of developing a <a href="https://www.healthline.com/health/nutrition-metabolism-disorders" target="_blank">metabolic disorder</a> by 17 percent. People with metabolic disorders have a higher chance of being diagnosed with high cholesterol, high blood pressure, and diabetes.</p><p>Rue suggests not carrying weights for your entire walk.</p><p>"Hand weights can give you an added level of energy burning, but you have to be careful with these because carrying [them] over a long period of time or while walking could actually lead to some overuse injuries," he says.</p>
Make It a Circuit<p>As another option, consider doing a circuit. First, put a pair of dumbbells on your lawn or somewhere in your home. Walk around the block once, then stop and do some bicep curls and tricep lifts before walking around the block again.</p><p>Rue recommends <a href="https://www.healthline.com/health/exercise-fitness/running-with-weights" target="_blank">avoiding ankle weights</a> during cardio workouts, as they force you to use your quadriceps rather than hamstrings. They can also cause muscle imbalance, according to the <a href="https://www.health.harvard.edu/staying-healthy/wearable-weights-how-they-can-help-or-hurt" target="_blank">Harvard Health Letter</a>.</p>
Find a Fitness Trail<p>Strength training isn't limited to weights. You can get stronger by <a href="https://www.healthline.com/health/bodyweight-workout" target="_blank">simply using your body</a>.</p><p>Often found at parks, fitness trails are obstacle courses with equipment for pullups, pushups, rowing, and stretches to build upper and lower body strength.</p><p>Try searching "fitness trails near me" online, checking out your local parks and recreation website, or calling the municipal office to <a href="https://calisthenics-parks.com/" target="_blank">find one</a>.</p>
Recruit a Friend<p>People who workout together stay healthy together.</p><p><a href="https://bmcgeriatr.biomedcentral.com/articles/10.1186/s12877-017-0584-3" target="_blank">One study</a> showed that older adults who exercised with a group improved or maintained their functional health and enjoyed their lives more.</p><p>Enlist the help of a walking buddy with a regimen you aspire to have. If you don't know anyone in your area, apps like <a href="https://www.strava.com/" target="_blank">Strava</a> have social networking features so you can get support from fellow exercisers.</p>
Try Meditation<p>According to the <a href="https://www.nccih.nih.gov/research/statistics/nhis/2017" target="_blank">2017 National Health Interview Survey</a>, published by the National Institutes of Health, meditation is on the rise, and for good reason.</p><p>Researchers <a href="https://pubmed.ncbi.nlm.nih.gov/29616846/" target="_blank">found</a> that mind-body relaxation practices can regulate inflammation, <a href="https://www.healthline.com/health/biological-rhythms" target="_blank">circadian rhythms</a>, and <a href="https://www.healthline.com/health/glucose" target="_blank">glucose</a> metabolism, as well as lower <a href="https://www.healthline.com/health/high-blood-pressure-hypertension" target="_blank">blood pressure</a>.</p><p>"Any form of exercise can be turned into a meditation of some type, either by the surroundings you are walking in, like a park or trail, or by blocking out the outside world with music on your headphones," Rue says.</p><p>You can also play a podcast or download an app like <a href="https://www.headspace.com/headspace-meditation-app" target="_blank">Headspace</a> that has a library of guided meditations to practice while you walk.</p>
Do Fartlek Walks<p>Typically used in running, fartlek intervals alternate periods of increased and decreased speed. These are <a href="https://www.healthline.com/nutrition/benefits-of-hiit" target="_blank">high-intensity interval training (HIIT)</a> workouts, which allow exercisers to accomplish more in less time.</p><p><a href="https://journals.plos.org/plosone/article?id=10.1371/journal.pone.0154075" target="_blank">One study</a> showed that 10-minute interval training improved <a href="https://www.healthline.com/health/metabolic-syndrome" target="_blank">cardiometabolic</a> health, or lowered the risk of heart disease, stroke, and diabetes, just as well as working out at a continuous pace for 50 minutes.</p><p><a href="https://journals.plos.org/plosone/article?id=10.1371/journal.pone.0111489" target="_blank">Research</a> also shows that HIIT workouts increase muscle <a href="https://www.healthline.com/health/fast-twitch-muscles" target="_blank">oxidative</a> capacity, or the ability to use oxygen. To do a fartlek walk, try walking at an increased pace for 3 minutes, slow down for 2 minutes, and repeat.</p>
Gradually Increase Pace<p>A faster walking pace is associated with a lower risk of <a href="https://www.healthline.com/health/copd" target="_blank">chronic obstructive pulmonary disease (COPD)</a> and respiratory diseases, according to a <a href="https://pubmed.ncbi.nlm.nih.gov/30303933/" target="_blank">2019 study</a>.</p><p>Still, it's best not to go from a stroll to an Olympic-worthy power walk in a day. Instead, increase your pace gradually to prevent injury.</p><p>"Start by walking at a brisk pace for about 10 minutes per day, 3 to 5 days per week," Rue says. "Once you've done this for a few weeks, increase your time by 5 to 10 minutes per day until you get to 30 minutes."</p>
Add Stairs<p>You've likely heard that taking the stairs instead of an elevator is a way to add more movement into your daily routine. It's also a way to step up your walking. Stair climbing has been shown to <a href="https://www.sciencedirect.com/science/article/pii/S2211335519301123?via%3Dihub" target="_blank">decrease the risk of mortality</a> and can easily add a bit more challenge to your walk.</p><p>If you don't have stairs in your home, you can often find them outside a local municipal building, train station, or at a high school stadium.</p>
Is Your Walk a True Cardio Workout?<p>Not all walks are equal. A walk that's too leisurely may not provide enough burn to qualify as cardio. To see if you're getting a good workout, try to <a href="https://www.healthline.com/health/how-to-check-heart-rate" target="_blank">measure your heart rate</a> using a monitor.</p><p>"A target goal for a good walking workout heart rate is about 50 to 70 percent of your maximum heart rate," Rue says, adding that maximum heart rate is <a href="https://www.healthline.com/health/fitness-exercise/fat-burning-heart-rate" target="_blank">typically calculated</a> by 220 beats per minute minus your age.</p><p>You can also monitor how easily you can carry on a conversation while you walk to gauge your heart rate.</p><p>"If you can walk and carry on a normal conversation, that's probably a lower intensity walk," says Rue. "If you are slightly breathless but can still have a conversation, that's probably a moderate workout. If you are out of breath and can't talk normally, that's a vigorous workout."</p>
Takeaway<p>By shaking up your routine, you can add excitement to your workout and reap even more rewards than a basic walk provides. Increasing the pace and intensity of a workout will make it more effective.</p><p>Simply pick your favorite variation to add some spice to your next walk.</p>
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