Tag Archives: Weight

Analysis of 19 million cats shows how our pets’ weight evolves throughout their lifetimes

New research is looking into how fat our cats are.

Orange cat.

Image credits Tasos Lekkas.

Fat cats — they’re definitely adorable. But, until now, we didn’t have any reliable way to tell if they’re getting too fat. New research based on over 54 million cat weight measurements hopes to establish a baseline body weight value that veterinarians and cat owners can use to gauge the health of domestic cats.

Chunky fur babies

“As humans, we know we need to strive to maintain a healthy weight, but for cats, there has not been a clear definition of what that is. We simply didn’t have the data,” said Prof. Theresa Bernardo, the IDEXX Chair in Emerging Technologies and Bond-Centered Animal Healthcare, the paper’s corresponding author.

“Establishing the pattern of cat weights over their lifetimes provides us with important clues about their health.”

The researchers from the University of Guelph’s Ontario Veterinary College (OVC) report that most cats keep putting on weight as they age, peaking at an average of eight years old. Another finding is that the average weight of our cats is also on the rise. The team looked at 54 million weight measurements recorded at veterinarian offices on 19 million different cats. They then broke this dataset down by gender, breed, and neutering status. The study is the first one to draw on such a large pool of data, and it provides important baseline information for owners and veterinarians.

Male cats tend to reach higher peak weights than females, and neutered or spayed cats tend to grow heavier than unaltered cats. Siamese, Persian, Himalayan, and Maine Coon breeds (who the team write are the four most-common purebred cat breeds), reached peak weight between 6 and 10 years of age. Your common domestic cats reached mean peak weight at around 8 years of age. Finally, the team notes that the mean weight of neutered, eight-year-old domestic cats increased between 1995 and 2005 but remained steady between 2005 and 2015.

“We do have concerns with obesity in middle age, because we know that can lead to diseases for cats, such as diabetes, heart disease, osteoarthritis and cancer,” said Dr. Adam Campigotto, the study’s lead author.

“Now that we have this data, we can see that cat weights tend to follow a curve. We don’t yet know the ideal weight trajectory, but it’s at least a starting point to begin further studies.”

Over half (52%) of the cats used in the study only had one body weight measurement on file, the team adds, which suggests that their owners either didn’t bring them back in for regular vet checkups or took them to a different veterinary clinic. The authors explain that it’s important to monitor weight changes in cats.

“Cats tend to be overlooked because they hide their health problems and they don’t see a vet as often as dogs do. So one of our goals is to understand this so that we can see if there are interventions that can provide more years of healthy life to cats,” Bernardo explains.

“The monitoring of body weight is an important indicator of health in both humans and animals. It’s a data point that is commonly collected at each medical appointment, is simple to monitor at home and is an easy point of entry into data-driven animal wellness.”

Campigotto advises pet owners who are concerned about their cat’s health or weight to buy a scale and form a habit of weighing the animal at home. He explains that weight gain or loss can be “an indicator of an underlying problem.” In the future, the team plans to analyze if automated feeders with built-in scales can be used to reduce cat obesity, in an effort to change “the emphasis to cat health rather than solely focusing on disease.”

The paper “Investigation of relationships between body weight and age among domestic cats stratified by breed and sex” has been published in the Journal of the American Veterinary Medical Association (AVMA).

New ‘brain training’ game could help you wean off of excess added sugar

Researchers at Drexel University, Pennsylvania want to help you cut down on excessive sugar consumption by playing a game.


Image via Pixabay.

The U.S. Department of Health and Human Services estimates that over half of American adults consume excessive amounts of added sugars, with detrimental effects to their health. A new study led by Evan Forman, Ph.D., a psychology professor at Drexel University’s College of Arts and Sciences, reports that computer games can be used to train players to wean off this sugar and help them to improve their health and manage their weight more easily.

Too sweet

“Added sugar is one of the biggest culprits of excess calories and is also associated with several health risks including cancer,” said Forman, who also leads the Center for Weight, Eating and Lifestyle Science (WELL Center) at Drexel.

“For these reasons, eliminating added sugar from a person’s diet results in weight loss and reduced risk of disease.”

The team developed and tested the efficiency of a “brain training game” that targets the brain area which inhibits our impulses. The aim was to train people to better resist the lure of foods with added sugars, specifically to decrease the consumption of sweets and sweet foods. Such systems have shown their efficiency in helping people quit other unhealthy habits, such as smoking. Forman says that this study is the first to look at how “highly personalized and/or gamified inhibitory control training” can help with weight loss using repeated, at-home training sessions.

In collaboration with Michael Wagner, a professor and head of the Digital Media department in Drexel’s Westphal College of Media Arts & Design and a group of digital media students, the team developed a game they named “Diet DASH”.

Diet DASH is built to integrate with each player’s particular habits. It automatically customized itself to focus on the sweets each participant tended to eat and adjusted its difficulty according to how well each player was resisting the temptation to eat said sweets. To test how well it worked, the team collaborated with a randomized group of 109 participants who were overweight and reported to over-enjoy sweets. Prior to starting the game, each participant took part in a workshop to help them understand why sugar is detrimental to their health and to learn which foods to avoid and methods for doing so.

“Prior to randomization, all participants attended a 2-h workshop in which they were provided with a dietary prescription (to eat only foods without added sugar or with very low amounts of added sugar, such as certain low-sugar breakfast cereals) as well as guidance in making dietary
modifications (e.g., reading food labels, shopping and cooking substitutions). Explanatory text, figures, and tables that allowed participants to easily identify targeted foods with added sugar were distributed,” the paper explains.

“The workshop helped give participants strategies for following a no-sugar diet. However, we hypothesized that participants would need an extra tool to help manage sweets cravings,” said Forman. “The daily trainings could make or break a person’s ability to follow the no-added sugar diet. They strengthen the part of your brain to not react to the impulse for sweets.”

Game screenshot.

Image credits Evan M. Forman et al., (2019), JoBM.

Each participant played the game for a few minutes every day for six weeks and then once a week for two weeks. The game itself places players in a grocery store, with the goal of putting the correct (healthy) food in a grocery cart as fast as possible while refraining from choosing incorrect food (their preferred sweets). Players were awarded points for correct items placed in carts.

Participants were randomly assigned to a highly-gamified version of the game (with better graphics and sounds) or a less-gamified version. The team reports that the gamification level didn’t seem to matter much as far as weight loss was concerned. However, the (few) male participants in the study reacted better to the highly gamified version than the women in the study.

Over half the participants in the study showed higher preferences toward sweets. For this group, the game helped them lose as much as 3.1% of their total body weight over eight weeks. Participants also rated how satisfactory they found the daily training, whether or not it became part of their daily routine, and whether they wished to continue with the training if it becomes publicly available.

“The study’s findings offer qualified support for the use of a computerized cognitive training to facilitate weight loss,” said Forman.

The WELL Center is now conducting a new trial with the highly gamified version of this training program specifically for men and is actively recruiting participants.

The paper “Computerized neurocognitive training for improving dietary health and facilitating weight loss” has been published in the Journal of Behavioral Medicine.

How birds stay slim even when they overeat

If you put a bird feeder in a populated area, you’ll likely see that most birds don’t shy away from a free snack. But despite all the extra food they may be munching on, the birds don’t really seem to get fat. It could be that all the fatter birds are eaten by predators, but if that were the case, then the over-eating behavior would likely be weeded out by evolution. So what’s going on? Why aren’t the birds getting fat?

Image credits: Alejandro Bayer Tamayo.

London environmental biologist Lewis Halsey found himself asking himself the very same question. He wanted to see whether songbirds regulate their activities to somehow consume more energy and stay slim.

“The passerine birds at the bird feeders near my home never seem to get fat despite having this buffet constantly available to them, but there are people who get heavy when exposed to that kind of all-you-can-eat environment,” says Halsey (@lewis_halsey), of the University of Roehampton.

Recent studies indirectly suggest that birds can adjust how much energy they derive from the food they ingest, but there still isn’t a very clear mechanism. So Halsey set out to do a literature review on the matter.

“For a given amount of food, an animal can unconsciously adjust how efficiently it uses the energy from it either behaviorally, for example by changing wingbeat frequency or singing patterns to use more or less energy, or physiologically, in terms of digestive or cellular metabolic efficiency,” Halsey says.

The results he found support this previous research. He says that we need to redefine the idea that calories are what goes through the mouth — instead, it’s not only what’s eaten but also the way the food is digested.

This, he explains, doesn’t only apply to birds — it can also be important for humans.

“We need to remember that ‘energy in’ isn’t what’s shoved down the beak but what’s taken up through the gut and then what’s extracted by the cells; looking at it as just the amount of food consumed is too simplistic,” he says. “And this goes for humans and other animals, not just songbirds.”

He says he wants to continue this research avenue in the future, by giving birds the equivalent of ice cream and observing if they still stay slim. He also wants to carry out more detailed lab experiments to assess exactly how this mechanism works. Perhaps, in time, it could be harnessed and ultimately replicated for medical treatments.

Journal Reference: Trends in Ecology & Evolution, Halsey: “Keeping Slim When Food Is Abundant: What Energy Mechanisms Could Be at Play?” https://www.cell.com/trends/ecology-evolution/fulltext/S0169-5347(18)30185-X

Losing sleep can lead to more extra pounds

Want to shed a few extra pounds? Here’s an idea, and it’s simple enough: try sleeping a bit more.

The link between sleep and obesity is not new — it’s been reported several times by researchers. A 2012 study found that lack of sleep can impact appetite regulation and impair glucose metabolism, while a 2011 review of studies found substantial evidence linking obesity and a lack of sleep. However, the exact nature of this link has not been thoroughly explained. A new study presents some of the most compelling evidence to date, showing that a lack of sleep encourages the body to store more fat, altering the body’s metabolism and an essential DNA function.

“Chronic sleep loss, social jet lag, and shift work—widespread in our modern 24/7 societies—are associated with an increased risk of numerous metabolic pathologies, including obesity, metabolic syndrome, and type 2 diabetes,” researchers explain in the new study. “Even minor weekly shifts in sleep timing, or as few as five consecutive nights of short sleep, have been associated with an increased risk of weight gain in healthy humans.”

Jonathan Cedernaes, a circadian researcher at Uppsala University in Sweden and lead author of the study says that sleep has an “irreplaceable” function, it’s not just to conserve energy and replenish our stamina. Yet many people tend to consider it an expendable resource — and this can have massive consequences.

Cedernaes and colleagues recruited 15 volunteers, who attended two testing sessions: once after a normal night’s sleep, and once after staying up all night. Biopsies and samples of fat, muscle tissue, and blood were also taken, and participants underwent a separate electroencephalography (EEG) and were asked to also complete sleep, food, and activity diaries as part of their screening.

The most significant change researchers note is in a gene activity called DNA methylation. The change was linked to cells increasing their tendency to absorb lipids, boosting the body’s ability to store fats. Furthermore, the participants’ muscle cells contained lower levels of structural proteins after a lack of sleep, suggesting a reduced ability to build and maintain muscles.

Lastly, scientists also report an increase in inflammation in the body after sleep deprivation, a major risk factor for type 2 diabetes, among others.

While previous studies have suggested a connection between obesity and sleep deprivation, this link was hard to separate from other lifestyle changes. Now, researchers have shown a physical mechanism that is responsible (or at the very least partially responsible) for this connection.

It should be said that the study featured a very small sample size and only analyzed a brief moment in the life of the participants. For the future, researchers call for more investigations to see what the effects of sustained sleep deprivation are on a wider segment of the population. But for now, it’s safe to say that sleep is not something you should be missing out on.

The study has been published in Science Magazine.

Eating quickly might favor weight gain, study suggests

Japanese researchers found a link between eating speed and weight gain. They interviewed almost 60,000 type 2 diabetes patients about their eating habits and then analyzed the data.

Credit: Pixabay/PublicDomainPictures

The satiety mechanism

When people eat too fast, hormones in the gut that relay the “I’m full” signal to the brain aren’t given enough time to work. This means you’ll eat more food, falsely believing you aren’t full yet. More calories result in weight gain.

As partially digested food enters the small intestine, a series of hormones are released into the bloodstream. Cholecystokinin (CCK), is released by the intestines in response to food consumed during a meal. Leptin, another hormone implicated in satiety, is an adiposity signal that communicates with the brain about long-range needs and satiety, based on the body’s energy stores. Research suggests that leptin amplifies the CCK signals, increasing the feeling of being full. By eating too fast, people may not give this intricate hormonal system the needed time to tell the brain that the stomach is full.

Eating slower lowers obesity development

Study authors Haruhisa Fukuda and Yumi Hurst of Kyushu University Graduate School of Medical Sciences in Fukuoka, Japan, confirm this hypothesis in their paper published in the journal BMJ Open.

Researchers measured the participants’ Body Mass Index (BMI) and waist circumference. Obesity is defined as 25 or more BMI points. Next, the participants answered a set of questions about their eating speed (‘fast’, ‘normal’ and ‘slow’), whether they had dinner within 2 hours of sleeping, but also habits concerning after-dinner snacking, skipping breakfast, alcohol consumption frequency, sleep adequacy and tobacco consumption.

The results showed that 21.5% of the slow-eating group was obese, compared to almost 30% of the normal-speed eaters and 45% of the fast-eating group. Slow eaters had an average BMI of 22, normal eaters had a BMI of approximately 23.5, and fast-eaters had an average BMI of 25. Waist circumference was found to be directly proportional to eating speed as well.

No sleep loss, not skipping breakfast and not eating dinner two hours before bed were all associated with a lower BMI.

This is an observational study because researchers did not measure calory intake and physical activity, which could have affected the results in an unknown manner.

Also, the terms ‘fast’, ‘normal’ and ‘slow’ were used by the participants of this study just as a self-evaluation, without a strict definition of the eating speeds, and without timing the participants while eating.

The verdict: eat slow and enjoy your meals, stop living your life on fast forward and take your time to savor the delish in your dish.

“Interventions aimed at altering eating habits, such as education initiatives and programmes to reduce eating speed, may be useful in preventing obesity and reducing the risk of non-communicable diseases,” the authors conclude.


Physical exercise is more important for health than weight, study reports

Overweight doesn’t have to mean unhealthy. New research shows that physical exercise can negate, even overcome, the negative health impact of weight even for the severely obese, even if you don’t lose weight.

Waist measure.

Image credits Michal Jarmoluk.

A new study led by Jennifer Kuk, associate professor at York University, found that individuals with severe obesity who partake in exercise and are fit have a health profile comparable to those who weigh significantly less. The research looked at the benefits of cardiorespiratory fitness for heart and circulatory system health in populations with mild to severe obesity.

The findings suggest that even individuals with a BMI over 40 (which is considered to be severely obese) can be fit and healthy, provided they engage in exercise.

“Obesity is only related with worse health in individuals who were unfit,” says Kuk. “We know that once you get beyond a BMI of 40, the risk of cardiovascular conditions increases exponentially so this study shows that having a high fitness level is still beneficial and it really reinforces the importance of fitness.”

She says that following physical activity guidelines, which recommend 150 minutes of exercise per week, generally only translates to half a pound of weight loss. However, despite the modest reduction in weight, this amount of exercise did translate to significant improvements in the health of those with severe obesity.

The team worked with 853 Canadian patients from the Wharton Medical weight management clinics in Southern Ontario. The participants underwent a clinical exam that included measurements of fasting blood sugar levels and maximal treadmill stress tests, which the team used as a baseline. The researchers compared these initial measurements to later ones taken during the weight management program to establish the effect of exercise on their overall health.

It took surprisingly little exercise (in the form of cardiovascular fitness) for the team to find meaningful improvements in the health of participants. Specifically, all those who avoided lagging behind in the lowest 20% fitness bracket (4 in 5 participants) were in good enough physical shape to see health improvements, the authors report.

“You really have to disconnect the body weight from the importance of fitness,” Kuk adds. “You can get fit without losing weight and have health benefits.”

Some 41% of the mildly obese participants had high fitness levels by the end of the programme, while 25% and 11% of participants with moderate and severe obesity respectively, had high fitness levels. Participants with severe obesity were more likely to have high blood pressure, as well as high glucose and triglyceride levels if they were in the lowest 20% fitness level bracket. However, they were not more likely to have these issues if they were in the top 80% fitness level bracket.

All in all, the results show that physical activity is much more important for the general health of people with severe obesity but, despite what that glam magazine might tell you, you don’t have to lose weight to be healthy — all you need to do is exercise and stay fit. And you can take heart in the fact that previous research has shown that you need much less physical activity to gain health benefits than to shed pounds.

So if all you want to do is to stay healthy, weight is a far less important factor than exercise. If your waistline is the bottom line, you’ll have to put in a few extra hours at the gym.


Humans got taller, then bulkier in ‘bursts’ during our evolution

Hominins have seen “pulses” of growth during their evolutionary history, followed by periods of “stagnation,” a new paper reports. This was the widest-scale study on the evolution of human stature and weight to date. Data was drawn from hominid fossils spanning the entire known evolutionary path of the genus. It reveals that over the last four million years, hominid stature and body mass have increased independently and at different speeds. Some extinct lineages even went through phases of shrinking.


Image credits Igor Ovsyannykov.

The paper drew on 311 specimens dating from roughly 4.4 million years ago (the time of the earliest known upright hominid species) through to the modern humans that followed the last ice age. It’s the largest study of hominid body size evolution to date, and the authors conclude that although this was a “long and winding road with many branches and dead ends,” the overarching pattern they’ve observed is one of bursts of growth followed by millennia of ‘stagnation’.

Taller, bigger, better

Earlier hominin evolution saw a wide range of body sizes, mostly owed to the number of different species and their particular evolutionary roots. Some were broad, ‘gorilla’-like, such as Paranthropus, or slimmer and agiler, as was Australopithecus afarensis. On average, hominins from four million years ago weighed a roughly 25kg and stood at 125-130cm tall. Observing how physicality evolved over time, however, the team reports at least three major “pulses” of significant changes.

The first one occurred as our own genus, Homo, made an appearance around 2.2-1.9 million years ago. This period saw an increase in both height (of about 20 cm) and weight (of between 15-20 kg).

Stature and height further separated about 1.4 to 1.6 million years ago, following the emergence of Homo erectus. Fossil evidence shows that hominid species living around this time grew taller by roughly 10 centimeters (3.93 inches) but wouldn’t significantly gain in body mass for another million years. This is the point where a familiar stature was reached. Body mass still remained lower on average than today.

It would take roughly one million years (around 0.5 to 0.4 million years ago) before heavier hominids made a consistent appearance in the fossil record. On average, hominid species saw a body mass increase of 10-15 kgs (22-33 pounds) about 500,000 years ago. This increase in body mass likely points to an adaptation to environments north of the Mediterranean.

Height and stature chart.

A and b show weight (kg, blue) and stature (cm, green) evolution over time, by geologic period and taxa, respectively. C and d show variations (in %) for weight and stature, by geologic period and taxa, respectively.
Image credits Manuel Will, Adrián Pablos, Jay T. Stock, 2017, RSOS.

“From then onwards, average body height and weight stays more or less the same in the hominin lineage, leading ultimately to ourselves,” says lead author Dr Manuel Will from Cambridge’s Department of Archaeology, and a Research Fellow at Gonville and Caius College.

There are a couple of exceptions, as is the case for Homo naledi and Homo floresiensis, which have in fact decreased in size over time, the team reports. However, this was likely due to their evolutionary roots in smaller-bodied ancestors, or the effect of evolutionary pressures acting on isolated and small populations. Floresiensis, for example, was discovered on an Indonesian island.

“Our study shows that, other than these two species, hominins that appear after 1.4m years ago are all larger than 140cm and 40kg. This doesn’t change until human bodies diversify again in just the last few thousand years.”

“These findings suggest extremely strong selective pressures against small body sizes which shifted the evolutionary spectrum towards the larger bodies we have today.”

Sizing up to the requirements

This tall to ride.

Image via NewStorkCity.

The findings could help us better understand what early hominids were up to. Initially, hominid height and weight largely evolved “in concert,” the team adds. The latter decoupling between height and bulk were likely caused by early humans’ migration out of the forest and as an adaptation to hunting in the savannah.

“An increase solely in stature would have created a leaner physique, with long legs and narrow hips and shoulders. This may have been an adaptation to new environments and endurance hunting, as early Homo species left the forests and moved on to more arid African savannahs.” Dr Will adds.

“The higher surface-to-volume ratio of a tall, slender body would be an advantage when stalking animals for hours in the dry heat, as a larger skin area increases the capacity for the evaporation of sweat.”

Later, as these populations moved further north and ran into colder climates, the increase in bulk would make them better at fighting the cold.

“The later addition of body mass coincides with ever-increasing migrations into higher latitudes, where a bulkier body would be better suited for thermoregulation in colder Eurasian climates.”

The results also suggest cladogenesis (lineage-splitting) may have played a part in increasing the average human’s height and mass. It’s possible that inter-species competition later drove the smaller-bodied lineage extinct. Sexual dimorphism — the physical distinction between genders, with mammalian females typically smaller than males — was also more prevalent in early hominid history, the authors added, and seems have become less emphasized.

However, Will says the theory should be taken with a grain of salt. It suits the available data very well, but there are vast gaps in the fossil record that the team has had to work around, ones that may have obscured the truth. He notes that at times, the team had to work on body size estimates starting from very fragmented remains, in some cases from as little as a single toe bone.

Overall, we know certain groups of humans have continued getting taller over the last century, most likely due to improvements in nutrition and healthcare. As these keep increasing, it’s likely that the average human stature is going to keep increasing.

“However, there is certainly a ceiling set by our genes, which define our maximum potential for growth,” said co-author Dr Jay Stock, also from Cambridge’s Department of Archaeology.

The paper “Long-term patterns of body mass and stature evolution within the hominin lineage” has been published in the journal Royal Society Open Science.

What is mass? Baby don’t weigh me – revamping the metrology of mass

The metric system is due for a mass makeover, as scientists are preparing to redefine four basic units by the end of 2018 in an effort to provide accurate measurements at all scales.

The shift will most notably affect the kilogram, the base measure of mass and the last member of the International System of Units still defined by a physical object. Current efforts are under way to check and fine-tune measurements of fundamental natural quantities — such as Avogadro’s number — for use in giving the kilogram a new mathematical definition.

The kilogram standard.
Image via itsoktobesmart

How do we define a kilogram, and how will this change?

Since 1889, the standard for mass has been a 1-kilogram cylinder of platinum and iridium metal at the Bureau International des Poids et Mesures in Sèvres, France. While this standard is handled carefully, it’s at risk of becoming dirty or damaged, says Michael Stock, a physicist at the French bureau.

“Any material object can change over time,” he says.

“It’s also hard to accurately scale this physical standard down to very small masses, like those of electrons,” added physicist David Newell of the National Institute of Standards and Technology (NIST) in Gaithersburg, Md.

Scientists aim to give the kilogram a new definition based on nature’s fundamental physical constants. This task requires a highly accurate measurement of Planck’s constant, which links energy and frequency. Planck’s constant can be used to measure and describe mass, as the two are mathematically linked through another natural constant, the speed of light.

The American kilogram standard.
image via nist.gov

Researchers are using the existing physical definition of a kilogram to measure Planck’s constant as accurately as possible. Then, this value can be set in stone and used to define mass in the future.

With devices known as watt balances, scientists can measure Planck’s constant directly using precisely known standards of mass and electrical current. Once Planck’s constant has been fixed, watt balances will then use Planck’s constant to calculate unknown mass.

A watt balance. And a dude.
Image credits Robert Rathe

In another approach, scientists count the number of atoms in extremely pure 1-kilogram silicon spheres. This method determines the number of atoms in a kilogram, which could be used to define the unit of mass. This technique also allows scientists to calculate a different fundamental value, the Avogadro constant (or Avogadro’s number). This constant describes the number, roughly 6.02 x 1023, of units per mole, the metric unit for amount of a substance. (A mole is the mass of a substance equal to its atomic or molecular weight expressed in grams.) A precise Avogadro constant can be used to calculate and confirm Planck’s constant.

When the new value and its uncertainty is averaged with previous calculations, the Avogadro constant comes out to 6.02214082 x 1023 per mole with an uncertainty of 18 parts in a billion, scientists report July 14 in the Journal of Physical and Chemical Reference Data. This number is just slightly smaller than the value of the constant currently described by NIST — 6.022140857 x 1023 per mole.

The watt balance and atom-counting techniques now give a nearly identical value of Planck’s constant, currently given by NIST as 6.6260704 x10-34 joule-seconds, with an uncertainty of under 20 parts in a billion, says metrologist Ian Robinson of the National Physical Laboratory in Teddington, England. Further measurements are still under way.

Where is the metric system headed?

In fall 2018, international delegates at a meeting of the General Conference on Weights and Measures will decide whether or not to approve the kilogram’s new definition. Based on existing plans, many believe the redefinition will happen at this time, Stock says, though nothing is guaranteed.

Because researchers’ careful calculations have accounted for the existing definition of mass, the redefinition should cause no perceptible shift in measurement.

“If we do our jobs right, nobody’s going to notice a thing,” Newell says. But future mass measurements should become stable, Robinson says.

While redefining the kilogram will be the most critical change ahead, Stock says, scientists also hope to redefine other units, including the mole and the kelvin, which measures temperature. These redefinitions will depend on fixing other constants, including the Avogadro constant. Making all of these changes at once will limit the number of times textbooks must be changed, Stock says.

The redefinitions won’t mark an end to the quest for a perfect metric system, Newell says.

“Metrologists are going to make the measurement exactly right. And the corollary is, they never finish their measurement.”