From the department of things you suspected were shady but somehow still feel unfair: Weight gain and weight loss are not the same for everyone. Some lucky people can subsist on refined carbs without putting on an ounce, while others obsess over calories, work out daily, and still never lose weight. Two recent studies suggest new ways in which dieting is rigged.
In the first paper, Israeli researchers determined that different people's bodies react to the same foods in ways that could lead to weight gain. For a study in the journal Cell, they gathered 800 healthy volunteers, hooked them up to blood-sugar monitors, and had them record all their meals in an app for one week. Everyone ate one of four standardized breakfasts for a smidgen of consistency.
The researchers expected that age and body-mass index would affect blood-sugar levels after meals, but they were surprised to find that certain foods, even seemingly innocent ones like tomatoes and bananas, regularly caused spikes in some people but not others. People with certain gut microbes also had higher blood-glucose responses. While no one gained weight during the short study period, the researchers point out that high blood-sugar levels are linked to diabetes, obesity, and heart problems. (They're working on a diet algorithm that can spit out meal plans tailored to your biology, but it will be years before it's ready for the general public.)
For a separate study published in the journal Nature Communication, researchers at the University of Cambridge first identified a protein, sLR11, that seems to inhibit the body’s ability to burn fat by restricting a process called thermogenesis. (This is the much-touted function of our brown fat cells, which burn fat to help keep us warm.) Then they looked at blood samples from 156 people and found that levels of the protein went up with increases in age, BMI, and visceral and subcutaneous fat. The authors suggested that the protein might prevent fat cells from burning too much fat during spikes in metabolism, making our bodies more efficient at holding on to fat over time. In other words, some people's bodies really cling to those fat cells, while some people's will shed them happily.
Whatever does one do now? We suggest demolishing your scale and embracing the caftan lifestyle of your dreams.