Five metabolic-health myths—busted

We dispel some of the most common misconceptions about metabolism and blood sugar to help you make healthier diet and lifestyle decisions

Written By

Rachel Nuwer


Article highlights

  • Eating smaller, frequent meals does not boost metabolism or aid weight loss compared to fewer, larger meals.
  • Glucose spikes, even in non-diabetics, can cause the same toxicity and insulin issues as chronically high glucose levels.
  • Sugar boosts energy temporarily but leads to a crash, while efficient fat-burning provides more sustained energy.
  • Natural sugars in fruits and juices can spike blood sugar just like added sugars if consumed in excess.
  • Even thin people with "healthy" BMIs can have poor metabolic health like insulin resistance and visceral fat.


News and social media are rife with health folklore, from colder weather causing colds to knuckle-cracking leading to arthritis. The last decade has seen an exponential increase in metabolic health research, but much of that learning has not yet become common knowledge, even to people trying to stay up on the latest information. Here we look at five persistent misconceptions about metabolic health.

The Myth: It’s better for my metabolism to eat lots of small meals throughout the day

In the age of pandemic-forced working from home, constant snacking has become a daily hazard. For some, though, this is a deliberate choice. Many people believe that eating smaller, more frequent meals throughout the day “boosts metabolism” and reduces hunger, which helps control weight. This idea was popular for decades, but there is no real science to back it up, says Dr. Bret Scher, a cardiologist and lipidologist in San Diego and medical director of Diet Doctor, a nutrition site focusing on healthy weight loss and low carb and keto diets.

“There’s an analogy that sugar is like the kindling on fire that catches really fast and burns really fast. Fat stores are the logs that burn slowly and longer.”

Dr. Bret Scher

A recent meta-analysis of studies in this area questions the notion that eating small meals throughout the day leads to weight loss. And if the myth were true, it would imply that eating less often would cause your metabolic rate to slow down and lead to weight gain. However, research shows that time-restricted feeding can reduce fat mass. Additionally, some studies suggest that frequent eating can cause glucose and insulin levels to remain elevated, with no chance to return to baseline levels. Consistently high insulin can block your body’s ability to burn fat and lead to insulin resistance. (It’s important to note that other studies show frequent eating lowered glucose levels; what you eat in those meals may matter more than how often you eat.)

The Myth: Glucose spikes are a normal part of my body processing sugar, and nothing to worry about

We do expect our blood sugar levels to fluctuate somewhat throughout the day. Food, exercise, mood, and sleep can all lead to a small rise and fall. But degree matters. Extreme glucose variability has been linked to heart disease, diabetes, and metabolic dysfunction.

Scher says having an average blood glucose level of 120 mg/dL a day but with variability that swings between 180 mg/dL and 70 mg/dL can have similarly toxic effects on metabolic health as having a persistently elevated blood sugar level of 150 mg/dL—a level consistent with Type 2 diabetes. “That type of variation is not a normal part of life,” Scher says.

In 2018, researchers used continuous glucose monitors (CGMs) to study blood sugar levels in 57 participants and found that individuals considered nondiabetic nevertheless experienced spikes in blood glucose to levels consistent with people with diabetes. Most often, this happened after the study participants ate high-carbohydrate meals.

Someone regularly spiking and crashing their glucose levels could still show a normal A1c or fasting glucose level on a test. But every time we spike glucose, we’re causing a flood of insulin release; over time, this can lead to insulin resistance.

The Myth: Sugar will give me an energy boost

Sugar may make you feel wired and jittery, but this effect is fleeting, and there is a definite cost: the sugar crash. As insulin rises and lowers blood sugar—often below a healthy baseline—you may feel shaky, foggy, or even hungrier than you were before the sugar binge. “It’s true that sugar can give a boost, but it’s probably not the energy boost you want,” Scher says. A 2019 meta-analysis of 31 studies representing data from nearly 1,300 adults found that sugar did not lead to an improvement in mood or alertness but instead seemed to trigger increased fatigue in the hour following sugar consumption.

A body adapted to efficiently burn fat, on the other hand, taps into a healthier and more dependable source of energy, Scher says. “There’s an analogy that sugar is like the kindling on fire that catches really fast and burns really fast. Fat stores are the logs that burn slowly and longer.” Lifestyle is key to accessing those long-lasting fat reserves. Exercising regularly, practicing intermittent fasting, and maintaining steady glucose levels all work over the long term to help your body adapt to efficiently burn stored fat rather than depend on quick fixes of sugar.

The Myth: I should only worry about added sugar, not natural sugar

Added sugars can affect a person’s blood sugar levels more than natural sugars in whole form. This is because natural sugars in their whole-food form tend to come with fiber, which slows the glucose absorption and can blunt a spike. The sugar still ultimately gets absorbed and has to be dealt with, though. “It’s not a free pass; it just makes it better than processed sugar,” Scher says. Additionally, refined fruits like those found in juice, which have been stripped of the fiber, can cause significant glucose rises. A 10-ounce bottle of Naked Juice’s Green Machine, for example, contains no added sugar but sports a whopping 35 grams of natural sugar, on par with many sodas.

In terms of parsing out acceptable levels of sugar intake, fruit can be especially confusing, Scher says, because it “has this aura around it that it’s uniquely healthy, so you should eat more.” While fruit can be a healthy part of a healthy person’s diet, fruit on its own, particularly if eaten many times per day, can keep glucose and insulin consistently elevated. And for someone who is overweight and insulin resistant, eating five servings of fruit a day can be downright unhealthy, Scher says.

The Myth: Thin people don’t need to worry about glucose or metabolic health

“The weight on the scale is not the ultimate judge,” Scher says. “Body composition is important.” People who have a “healthy” weight can still have a high percentage of fat and a low percentage of lean mass. This is often because of visceral fat, which forms within the abdominal cavity around organs, and is more dangerous to health than subcutaneous fat (the fat just below the skin).

Although obesity is associated with insulin resistance, even people with “healthy” body weight can have poor metabolic health, which can lead to insulin resistance and other markers of metabolic syndrome, a group of conditions that increase the risk of heart disease, stroke, and diabetes. A 2020 review, for example, found that those who are metabolically unhealthy but have a normal body weight often possess excess visceral body fat.

“Healthy”-weight individuals comprise around 10 to 15 percent of those with Type 2 diabetes, often categorized as “lean diabetes,” with non-white populations at higher risk. Genetics is the strongest predictor of lean diabetes, with people who have at least one parent with lean diabetes being 40 percent more likely to develop the condition. But lifestyle choices—including diet, poor sleep, alcohol, smoking, and a lack of exercise—can also contribute.