Skip to content

One Major Side Effect Losing Weight Could Have on Your Immunity, New Study Says

New research offers a reminder about how important it is not to go too hard with a diet.

The conversation around dieting is gradually changing. You might agree that it's positive to see the world embracing healthier notions about weight loss, such as Adele's recent stance that losing weight should be a byproduct of overall good self-care. Now, a new study seems to support this milder, more modern attitude toward getting trimmer—because, as the researchers' experiment has shown, aggressive food restriction might cause some dieters to become more susceptible to catching illnesses.

Keep reading to learn more about the findings—and, for more on the link between eating and your health, check out The #1 Food Putting You At Risk of Heart Disease, Says Science.

The Study Sample

leftover food

A new Iranian study published in the American Journal of Translational Research aimed to evaluate whether significant calorie restriction would affect the immune system. To achieve this, a team of doctorate clinicians specializing in nutrition and public health gathered 29 female participants who were overweight, with body mass index greater than 30 kg/m² (which is the benchmark the American Heart Association considers obese).

The Factors


The researchers divided the 29 women into two groups. The experimental group went on medication for weight loss, in addition to going on a diet that called for them to consume 600 fewer calories per day than the standard caloric requirement.

The other group of participants were able to eat freely.

 Eating This One Type of Food Could Slash Your Alzheimer's Risk, New Study Finds

The Measurements


Both at the start of the experiment and after the experimental group had lost 10% of their body weight, the researchers measured the number of lymphocytes (a type of white blood cell that supports the body's immune function) in each of the participants.

They state that for women who underwent calorie restriction and medication to lose 10% of their body weight, their "natural killer cells"—cells that are key to the body's immune system—decreased.

Meanwhile, for the control group that ate freely, the researchers report that no significant changes were observed in the immune markers that were measured.

 The Verdict on Taking Vitamin D Supplements for Your Immunity

What It Means

Overweight Asian woman wearing yellow orange dress relaxing in the park.

Of their findings, the researchers conclude: "Caloric restriction-induced weight loss might independently weaken the antiviral immune defense." They note that further clinical trials on the subject are warranted.

You should always talk with your licensed healthcare provider before starting out on a new wellness plan. But for the purpose of this report, this study shouldn't discourage you from losing weight to reach a size that's healthier for you.

However, minding both nutrition and physical activity are jointly important focuses in your weight loss journey. And perhaps most importantly, as this study may be interpreted to convey, eating fewer calories than experts suggest are healthy may help you slim down… but in other ways, it could prove detrimental to your health.

Get more food and wellness news here:

Krissy Gasbarre
Krissy is a senior news editor at Eat This, Not That!, managing morning and weekend news related to nutrition, wellness, restaurants and groceries (with a focus on beverages), and more. Read more about Krissy