Space is an unnatural environment for humans. We can’t survive unprotected in a pure vacuum for more than two minutes. Getting to space involves being strapped to a barely contained chemical explosion.

Since 1961, fewer than 700 people have been into space. Private space companies such as SpaceX and Blue Origin hope to boost that number to many thousands, and SpaceX is already taking bookings for flights to Earth orbit.

I’m an astronomer who has written extensively about space travel, including a book about our future off-Earth. I think a lot about the risks and rewards of exploring space.

As the commercial space industry takes off, there will be accidents and people will die. Polaris Dawn, planned to launch early in September 2024, will be a high-risk mission using only civilian astronauts. So, now is a good time to assess the risks and rewards of leaving the Earth.

Space travel is dangerous

Most Americans vividly recall the disasters that led to the loss of 14 astronauts’ lives. Two of the five space shuttles disintegrated, Challenger in 1986 soon after launch and Columbia in 2003 on reentry.

In total, 30 astronauts and cosmonauts have died while training for or during space missions.

There have also been dozens of close calls. Two astronauts are currently staying on the International Space Station for an extra six months because NASA declared their Boeing Starliner vehicle unsafe for the return journey. Starliner has had many problems during its development, including flammable tape, stuck valves and inadequate parachute systems. But a critical thruster malfunction is what caused NASA to abandon it as a return vehicle.

It’s not always safe on the ground, either. In addition to the three Apollo 1 astronauts who died in a 1967 launch pad fire, about 120 people died in the launchpad explosion of an unmanned rocket in Russia in 1960, and hundreds died in 1996 when a Chinese rocket veered off course and crashed into a nearby village.

The fatality rate of people traveling in space is about 3%. That sounds low, but it’s higher than extreme sports such as BASE jumping or jumping off a cliff wearing a wingsuit. The only recreations that rival the risk of space travel are solo free-climbing and climbing above 19,685 feet (6,000 meters) in the Himalayas.

Civilians in space

The 2020s have kicked off the era of civilian astronauts. After the death of schoolteacher Christa McAuliffe in the Challenger disaster, NASA stopped sending civilians into space. But for commercial space companies, it’s part of the business model.

The first all-civilian crew to reach orbit rode a SpaceX Dragon spacecraft in 2021, the Inspiration 4 mission. Since 2020, 69 private astronauts have gone to space, although only 46 reached the Kármán line – the formal definition of the edge of space.

The commercial space industry’s safety record is not perfect. No civilian has died in space, but one pilot died and another was seriously injured in a test flight of Virgin Galactic’s SpaceShipTwo craft in 2014. This accident followed three deaths and three injuries in an explosion during a prelaunch test of the SpaceShipTwo rocket in 2007.

SpaceX, the largest commercial space company with 13,000 employees and a market value of US$180 billion, has seen no fatalities in flight, but it has recorded one death and hundreds of injuries in the workplace.

The Polaris Dawn mission was planned to launch Aug. 27, 2024, though a helium leak and bad weather has delayed it. It will push the envelope of risk for civilians in space. This SpaceX flight will reach an altitude of 435 miles (700 kilometers), higher than any astronauts since Apollo.

The Polaris Dawn’s four-person civilian crew will receive a hefty dose of radiation, getting as much in a few hours as they would in 20 years on the Earth. NASA is doing research to understand the extent of the health risks from radiation.

The mission will also include a spacewalk – the first for nongovernment astronauts. It will use spacesuits never tested in space. Since the spacecraft they’re using – the SpaceX Dragon – has no airlock, the inside of the capsule will be exposed to the vacuum of space, with all the crew members wearing spacesuits.

Russian cosmonaut Alexei Leonov nearly died during the first spacewalk in 1965, and other spacewalks have led to temporary blindness, near drowning and nearly being lost in space forever. A spacesuit is like a miniature spacecraft, and it has to withstand rapid temperature changes of hundreds of degrees when moving in and out of direct sunlight. Even a small tear or puncture can be fatal.

But while space travel comes with dangers, it also has rewards. Since Polaris Dawn will travel higher than any previous mission that did not go to the Moon, the crew will be able to do research on high-radiation environments. They will investigate the effects of spaceflight on the human body and evaluate how future deep-space travelers might diagnose and treat themselves.

A less tangible but potentially profound benefit is the overview effect – many astronauts report a feeling of awe from experiencing the Earth from space.

Space boom

Space is booming – hopefully just metaphorically and not literally. SpaceX makes money by launching Starlink satellites and ferrying supplies and people to the International Space Station, with estimated revenues of $15 billion this year. Blue Origin sells rocket engines and has contracts with NASA.

Both companies sell rides into space to high-net-worth individuals, but that’s a small fraction of their revenues. Space tourism is not available to the masses yet. Virgin Galactic offers a short, suborbital ride for $450,000, but getting to Earth orbit will cost you $55 million.

The space tourism market was $750 million in 2023, and that’s projected to grow to $5.2 billion over the next decade. Reusable rockets have made the cost of launching a spacecraft 10 times cheaper than it was a decade ago.

For space tourism to take off with a demographic broader than multimillionaires and thrill-seekers, it needs to be safe – both in perception and in reality. Many space entrepreneurs expect space travel to follow aviation’s arc, which also started by attracting rich people and thrill-seekers.

Since 1930, improvements in technology and safety features have lowered the number of fatal accidents in the aviation industry per million miles flown by a factor of 3,000. A more realistic target may be to make space travel as safe as driving. That’s a more lenient target, since driving is more dangerous than flying. Your annual odds of dying in a car crash are 1 in 5,000, compared with annual odds of 1 in 11 million of dying in a plane crash.

In the United States, the government has kept regulations light on the commercial space industry to encourage entrepreneurs.

Elon Musk’s dreams of millions of passengers and a city on Mars may not become reality. But if the cost of a jaunt to Earth’s orbit comes down to the cost of a high-end cruise, many people could experience the thrill of weightlessness and of seeing the Earth as a beautiful planet from above.

Chris Impey, University Distinguished Professor of Astronomy, University of Arizona

This article is republished from The Conversation under a Creative Commons license. Read the original article.

Is the adage “calories in, calories out” true? The short answer is yes, but the full story is more nuanced.

From the moment food touches your tongue to the time it leaves your body, your digestive system and gut microbiome work to extract its nutrients. Enzymes in your mouth, stomach and small intestine break down food for absorption, while microbes in your large intestine digest the leftovers.

“Calories in, calories out” refers to the concept that weight change is determined by the balance between the calories you consume and calories you expend. This includes not only the number of calories you eat due to appetite and absorb via digestion, but also how well those absorbed calories are burned through metabolism.

Recent research indicates that a significant factor influencing people’s variable appetites, digestion and metabolism are biologically active leftover components of food, known as bioactives. These bioactives play a key role in regulating the body’s metabolic control centers: your brain’s appetite center, the hypothalamus; your gut’s digestive bioreactor, the microbiome; and your cells’ metabolic powerhouses, the mitochondria.

I’m a gastroenterologist who has spent the past 20 years studying the gut microbiome’s role in metabolic disease. I’ll share how dietary bioactives help to explain why some people can eat more but gain less, and I’ll offer some dietary tools to improve metabolism.

Ruminating on appetite and digestion

Research has shown that consuming whole foods still “packaged” in their original fibers and polyphenols – the cellular wrappers and colorful compounds in plants that confer many of their health benefits – leads to more calories lost through stool, when compared with processed foods that have been “predigested” by factories into simple carbs, refined fats and additives.

This is one way calorie-free factors influence the “calories in, calories out” equation, which can be beneficial in a society where calorie intake often exceeds needs. Eating more whole foods and less processed foods simply lets you eat more because more of those unprocessed calories go out the other end unused.

Fiber and polyphenols also help regulate your appetite and calorie intake through the brain. Your microbiome transforms these leftover bioactives into metabolites – molecular byproducts of digestion – that naturally decrease your appetite. These metabolites regulate the same gut hormones that first inspired the popular weight loss drugs Wegovy, Ozempic and Mounjaro, controlling appetite through your brain’s satiety center, the hypothalamus.

Processed foods lack these bioactives and are further formulated with salt, sugar, fat and additives to be hyperpalatable, causing you to crave them and eat more.

Mitochondrial maestros in the middle

A full accounting of calories also depends on how effectively your body burns them to power your movement, thoughts, immunity and other functions – a process largely orchestrated by your mitochondria.

Healthy people typically have high-capacity mitochondria that easily process calories to fuel cellular functions. People with metabolic diseases have mitochondria that don’t work as well, contributing to bigger appetites, less muscle and increased fat storage.

They also have less of a mitochondria-rich type of fat called brown fat. Rather than storing calories, this fat burns them to produce heat. Less brown fat may help explain why some people with obesity can have lower body temperatures than those who aren’t obese, and why there has been a decline in average body temperature in the U.S. since the industrial revolution.

Healthy mitochondria that burn more calories might also help explain why some people can eat more without gaining weight. But this raises the question: Why do some people have healthier mitochondria than others?

Your mitochondrial health is ultimately influenced by many factors, including those usually associated with overall well-being: regular exercise, adequate sleep, stress management and healthy eating.

Who turned off the metabo-lights

The latest nutrition research is revealing the roles that previously underappreciated dietary factors play in mitochondrial health. Beyond the essential macronutrients – fat, protein and carbohydrates – and micronutrients such as vitamins and minerals, other leftover factors in food, including fibers, polyphenols, bioactive fats and fermentation products, are also key for metabolism.

Unlike a Western diet, which often lacks these bioactives, traditional diets such as the Mediterranean and Okinawan diets are rich in foods – nuts, seeds, fruits, vegetables, whole grains and fermented foods – replete with these factors. Many bioactives pass undigested through the small intestine to the large intestine, where the microbiome converts them into activated metabolites. These metabolites are then absorbed, influencing the number of mitochondria in cells and how they function.

At the most fundamental level of cell biology, metabolites turn on and off molecular switches in your genes through a process called epigenetics that can affect both you and your offspring. When the metabolic “lights” are turned on, they enliven the mitochondria responsible for a faster metabolism, effectively increasing the calories you use.

Please mind the microbiome gap

A healthy microbiome produces a full range of beneficial metabolites that support calorie-burning brown fat, muscle endurance and metabolic health. But not everyone has a microbiome capable of converting bioactives into their active metabolites.

Long-term consumption of processed foods, low in bioactives and high in salt and additives, can impair the microbiome’s ability to produce the metabolites needed for optimal mitochondrial health. Overuse of antibiotics, high stress and lack of exercise can also adversely affect microbiome and mitochondrial health.

This creates a double nutrition gap: a lack of healthy diet and a deficiency in the microbes to convert its bioactives. As a result, well-studied nutritional approaches such as the Mediterranean diet might be less effective in some people with an impaired microbiome, potentially leading to gastrointestinal symptoms such as diarrhea and negatively affecting metabolic health.

In these cases, nutrition research is exploring the potential health benefits of various low-carb diets that may bypass the need for a healthy microbiome. While the higher protein in these diets can reduce the microbiome’s production of beneficial metabolites, the lower carbs stimulate the body’s production of ketones. One ketone, beta-hydroxybutyrate, may function similarly to the microbiome metabolite butyrate in regulating mitochondria.

Emerging microbiome-targeting approaches might also prove helpful for improving your metabolic health: butyrate and other postbiotics to provide preformed microbiome metabolites, personalized nutrition to tailor your diet to your microbiome, intermittent fasting to help repair your microbiome, and the future possibility of live bacterial therapies to restore microbiome health.

Tools to transform fat into fuel

For most people, restoring the microbiome through traditional diets such as the Mediterranean diet remains biologically achievable, but it is not always practical due to challenges such as time, cost and taste preferences. In the end, maintaining metabolic health comes back to the deceptively simple healthy lifestyle pillars of exercise, sleep, stress management and nutritious diet.

Some simple tips and tools can nonetheless help make nutritious diet choices easier. Mnemonics such as the 4 F’s of food – fibers, polyphenols, unsaturated fats and ferments – can help you focus on foods that best support your microbiome and mitochondria with “leftovers.” Bioactive-powered calculators and apps can also aid in selecting foods to control your appetite, digestion and metabolism to rebalance your calorie “ins and outs.”

Christopher Damman, Associate Professor of Gastroenterology, School of Medicine, University of Washington

This article is republished from The Conversation under a Creative Commons license. Read the original article.