Obesity and malnutrition are not mutually exclusive

Evidence suggests malnutrition counteracts ‘obesity paradox’.


Picture a malnourished hospital patient.

The person you're imagining probably doesn't weigh 300 pounds, does she? Yet obese patients can develop malnutrition, before or during hospitalization, and have worse outcomes as a result.

Photo by Thinkstock
Photo by Thinkstock

In fact, according to a recent study, malnutrition counteracts the “obesity paradox,” which holds that, among the critically ill, heavier patients do better than normal- or underweight patients. Researchers who looked specifically at malnourished obese patients showed that they had a higher risk of mortality than well-nourished patients of similar body mass index, according to results published in the January issue of Critical Care Medicine.

Yet these patients' nutritional deficiencies often pass under hospital clinicians' radar, according to experts. “We as physicians don't necessarily have a great handle on who is malnourished,” said Kenneth B. Christopher, MD, co-author of the study. “You can always tell if someone's profoundly malnourished, because they start appearing to be cachectic, but it's less severe degrees of malnutrition that are actually harder to see.”

In addition to judgments based on appearance, a number of other factors can make it difficult to diagnose or prevent malnutrition in obese inpatients, including shortcomings in history taking, limitations of lab testing, and challenges in nutrition delivery.

Hospitalists can help correct these deficits, according to experts, by raising their own index of suspicion and working with the health care team to focus on patients' nutritional status.

Pre-existing malnutrition

Accurate screening for malnutrition begins with the recognition that you can't see it with your eyes, or even a scale. “Nutritional status is not body mass index,” summarized Dr. Christopher, who is a nephrologist and critical care specialist at Brigham and Women's Hospital in Boston.

For one thing, excess weight may not represent body fat. “A lot of hospitalized patients have high weights, but a lot of times it's just due to edema and excess water,” said Jeffrey Mechanick, MD, FACP, a professor of medicine in the division of endocrinology at Mount Sinai Hospital in New York City.

Obesity could also distract from recent weight loss, an important marker of malnutrition. “Somebody could be obese but have a gastrointestinal problem and have been losing weight. Even though they've lost a considerable amount of weight, they started off so obese, that they're still technically obese,” said Dr. Mechanick.

Patients may not think to bring this issue to a clinician's attention. “It may take longer for them to come to terms that the weight loss is a red flag for something going on, because our society has so much stigma around overweight and obesity that when many obese people lose weight, however they lose it, they get more positive feedback,” said Charlene W. Compher, PhD, a professor of nutrition science at the University of Pennsylvania in Philadelphia.

If a patient lost weight due to bariatric surgery, he is particularly at risk for malnutrition. “The odds of having vitamin deficiencies are very high with patients with gastric bypass, especially if they do not take all of the vitamin and mineral supplements that they are instructed to,” said Dr. Compher.

And any obese patient could be getting enough calories, but not enough protein or other nutrients, due to an unhealthy diet. “Do they live on fast food or high-calorie but poor nutrition foods?” said Lisa Kirkland, MD, FACP, a hospitalist at Mayo Clinic in Rochester, Minn., and a critical care specialist at Abbott Northwestern Hospital in Minneapolis.

As her question indicates, history-taking is key to uncovering malnutrition risk. One of the most important questions to ask is whether the patient has lost 10% or more of her body weight in the past 6 months.

“This is a good number to keep in your mind: 10% recent weight loss,” said M. Molly McMahon, MD, an endocrinologist and professor of medicine at Mayo Clinic in Rochester. Studies have shown poorer outcomes in hospitalized patients with that degree of weight loss, she reported. Patients who are fluid-expanded may also be malnourished without documented weight loss, she noted.

Hospitalists themselves don't have to do the asking, but they should pay attention to the answers. “All hospitals in the country are expected to have nutritional screening, which is usually done by the admitting nurse,” said Dr. Kirkland. “Just screening and saying, ‘Here's an assessment of the patient's malnutrition’ is not enough….The first line of action is the hospitalist involving the dietitian to assess the patient and create a plan, and to monitor the patient to make sure that they're making progress.”

Calling in a dietitian is a necessity when malnutrition is suspected, agreed Dr. Compher. “They have specific skills and training but also they take more time to find out details of the weight loss history, the pattern of food intake—details that might give you the idea that they've had a vitamin deficiency or something going on,” she said.

It may be tempting to turn to laboratory tests to answer these questions for you, and tests can be helpful to uncover specific vitamin deficiencies, but they don't help with general malnutrition.

“There's no lab test for malnutrition,” said Dr. Kirkland. “People rely on albumin. It's not helpful for malnutrition. Albumin just reflects the acuity of illness or the duration of malnutrition, but not the severity of it or the presence of it.”

Becoming malnourished

Lab measurements are even less helpful for the next challenge in inpatient nutrition: keeping patients who start out nourished from developing malnutrition during hospitalization. “When an obese person gets sick, they are at risk of the same protein-wasting that comes from acute illness [as] a non-obese person,” said Dr. Kirkland.

In addition to the illness process, hospital processes may cause malnutrition. “Patients are made NPO to go to procedures. [Or] there are logistical problems, and even though you order the correct prescription [of nutrients], they simply don't get it,” said Dr. Mechanick.

Divisions of responsibility can make it easy for clinicians to overlook the fact that their patients aren't receiving enough nutrition. “Many times the dietitians don't even see the patient's tray because the nurse takes it away, so they kind of assume that the patient is eating what they're getting,” said Dr. Kirkland.

Such problems can be exacerbated for obese patients by common misconceptions, such as “if you're obese, you don't really need to be fed, because you have these tremendous reserves,” said Dr. Christopher.

Even the experts have uncertainty about how to assess and meet these patients' energy requirements, though. “We need to learn much more about caring for hospitalized patients who are overweight or obese because two-thirds of the country fits into those categories,” said Dr. McMahon.

Calculating calories

In Europe, the popular solution is indirect calorimetry, which uses oxygen consumption and carbon dioxide production to calculate energy expenditure. But fewer U.S. hospitals have the technology, which has yet to be proven cost-effective, according to Dr. Mechanick. “We need better tools to assess energy requirements, particularly in the ICU,” he said.

In the interim, most clinicians use calculations, like the Harris-Benedict equation, but there are still uncertainties about how these work for patients who are very far from their ideal weight. “Obese people vary in how much of their body weight is muscle mass and how much is fat mass,” said Dr. Compher.

Once you've calculated how many calories a patient typically consumes, there are additional questions about how many to provide during hospitalization. “You have to feed them enough to meet their needs, but there's some evidence that particularly in the critically ill, if you feed under their needs, or under their estimated needs, that they have a better outcome,” said Dr. Kirkland.

The concept has been called permissive underfeeding or hypocaloric feeding, but it should really be thought of as appropriate feeding, according to Dr. Mechanick. The idea is that in some patients, including many obese ones, “it is desirable that they burn off some of their fat stores as a source of energy, so you really want to avoid overfeeding,” he said.

But if you do underfeed, also avoid giving too little protein. “When patients are permissively underfed, it is critical to provide adequate protein,” said Dr. McMahon.

Cancer patients generally shouldn't be put on hypocaloric diets, and high-protein diets can be a problem for some patients with liver function limitations, Dr. Compher noted.

The whole concept is still somewhat unproven, she warned. “There are not a lot of data to support hypocaloric, high-protein diets. Most of the data that exist either are very, very old or come from the ICU setting,” said Dr. Compher.

There's a general lack of definitive data in the nutrition field, multiple experts agreed. Having established that malnutrition is bad for obese inpatients, Dr. Christopher is studying whether hospital clinicians can do anything to correct that. “We don't yet know whether or not an intervention can help push these patients from a malnourished state to a nourished state,” he said. “If patients are better fed, we may be able to at least attenuate some of the risk of malnutrition that can develop in a hospitalized patient.”

In many cases, the effort to get patients properly nourished will need to continue after discharge. “The patients that we have in the hospital today are so critically ill that it's challenging for them to attend to very much education. They generally do better when that is presented to them at a later time when they're feeling better,” said Dr. Compher.