Just in time for the New Year, when everyone’s making their resolutions, we’ve got some major news on the health front. If your goal is to get healthy in 2016, listen up: What may be super healthy for others may be total junk food for you.

An Israeli study published in Cell asked 800 volunteers to complete surveys about their health habits and lifestyle choices. Their bodies were also measured, and they were administered blood tests. The researchers, who were from the Weizmann Institute of Science, asked these volunteers to record their sleep, exercise, and diet over the course of a week, and they were administered under-the-skin monitors that measured their glucose levels every five minutes.

According to the research, our bodies process food in incredibly different ways, meaning that some foods that are deemed “healthy” aren’t for certain people, and some known unhealthy foods are healthy for others. Certain foods are considered to have a high glycemic index (GI)—they make blood sugar spike more than others, and thus are considered unhealthy; however, the study found that foods don’t have a set GI value for everyone because metabolization is a personalized affair.

“Most dietary recommendations that one can think of are based on one of these grading systems,” Eran Segal, one of the study’s researchers, told CNN. “However, what people didn’t highlight, or maybe they didn’t fully appreciate, is that there are profound differences between individuals. In some cases, individuals have opposite responses to one another, and this is really a big hole in the literature.”

For example, one woman who suffers from pre-diabetes and obesity has been trying various diets over the course of her life, but her healthy eating habits have had no effect. She learned from the study that tomatoes — typically considered quite healthy — actually spike her blood sugar levels considerably, which could be contributing to her inability to lose weight, as she eats them often.

“For this person, an individualized tailored diet would not have included tomatoes, but may have included other ingredients that many of us would not consider healthy, but are in fact healthy for her,” Eran Elinav, of Weizmann’s Department of Immunology, told CNN. “Before this study was conducted, there is no way that anyone could have provided her with such personalized recommendations, which may substantially impact the progression of her pre-diabetes.”

Elinav concluded that these results could mean “that there are likely many people out there who have been thinking they’re failing to lose weight despite their healthy diets, when it actually is because of their healthy diets.”

But don’t toss your salad fixings into the garbage just yet. What we can learn from this study is that we shouldn’t take nutrition recommendations at face value, but rather keep a journal of what we eat, our energy levels, our weight, and how we feel in general. This way, we can see if there’s some sneaky “health” food we’ve been eating that our body doesn’t process well.

(Image via Shutterstock.)