What Are Ensure Drinks For? Uses, Benefits & Side Effects

Ensure drinks are oral nutritional supplements designed to fill calorie and nutrient gaps when a person cannot meet their needs through regular food alone. They are most commonly used for older adults at risk of malnutrition, patients recovering from surgery or illness, and people with conditions that make eating difficult, though they have also become popular among a much wider group of consumers looking for convenient nutrition. The clinical evidence behind these products is surprisingly robust for some uses and thin for others, and the gap between marketing claims and medical reality is worth understanding before you grab a case off the shelf.

The Core Purpose of Oral Nutritional Supplements

Ensure falls into a category called oral nutritional supplements, or ONS. These are commercially prepared, nutrient-dense liquids meant to be consumed alongside regular meals or, in some cases, as a temporary meal replacement. They typically provide a controlled mix of protein, carbohydrates, fat, vitamins, and minerals in a ready-to-drink format. The original clinical rationale is straightforward: when someone is losing weight, eating poorly, or recovering from a medical event, getting enough calories and protein through food can be genuinely difficult. An ONS bridges that gap without requiring the person to chew, prepare, or even feel particularly hungry.

The most common clinical scenarios where doctors and dietitians recommend Ensure or similar products include involuntary weight loss in older adults, cancer-related appetite loss, post-surgical recovery when solid food is poorly tolerated, and chronic conditions like COPD or heart failure that raise calorie demands while suppressing appetite. They are also used for people with swallowing difficulties, though texture-modified food-based alternatives exist for that group as well.

What the Evidence Shows for Malnourished Older Adults

The strongest evidence for ONS use involves older adults who are malnourished or sliding toward it. A study of community-dwelling elderly people found that daily ONS use significantly increased protein intake, body weight, grip strength, and walking speed compared to baseline values.¹ Quality-of-life scores improved across all measured dimensions as well. A separate randomized controlled trial in older adults with malnutrition found that 12 weeks of ONS combined with a regular diet significantly improved nutritional status, biochemical markers, and daily energy and macronutrient intake compared to the control group.²

These findings matter because malnutrition in older adults is easy to miss. It does not always look like dramatic weight loss. Subtle declines in muscle mass, reduced appetite, slower recovery from minor illness, and increased fatigue can all signal that nutritional intake has fallen below what the body needs. By the time a person looks visibly underweight, the problem is often already serious.

Hospital Readmissions and Length of Stay

One of the more compelling findings in the ONS literature involves what happens after hospitalization. A study at a US academic medical center found that malnourished patients who received ONS had roughly 39% fewer 30-day readmissions compared to similar patients who did not receive supplements. The benefit was even larger for cancer patients, who saw a 46% reduction in readmissions. Getting supplements to patients sooner also mattered: cutting the time from admission to first ONS dose in half was associated with a meaningful decrease in hospital length of stay across general, oncology, and intensive care populations.³

These are observational findings rather than results from a blinded trial, so some caution is warranted. Patients who accept and consume supplements may differ in motivation or overall health trajectory from those who do not. Still, the effect sizes are large enough and consistent enough across patient subgroups that most hospital nutrition guidelines now recommend early ONS for patients identified as malnourished or at nutritional risk.

Muscle Health and Sarcopenia Prevention

As people age, they gradually lose muscle mass and strength, a process that accelerates after about age 65. When this decline crosses a clinical threshold, it becomes sarcopenia, which raises the risk of falls, fractures, disability, and even death. Protein intake plays a direct role in slowing or partially reversing this process, and ONS products are one vehicle for delivering that protein.

An expert consensus from the Asian Working Group for Sarcopenia reviewed trials of protein supplementation in older adults and found that most forms of protein supplementation, including whey protein and ONS formulations, were associated with significantly greater improvements in muscle strength, muscle mass, and physical performance compared to controls.⁴ The effective protein doses in successful trials typically ranged from about 40 to 60 grams per day, divided across multiple servings. That is more than what a single bottle of Ensure provides, so people using ONS specifically for muscle health usually need to combine it with protein from meals or consume multiple servings.

The HMB Formulation and What It Adds

Some Ensure products, like Ensure Plus Advance, contain an ingredient called beta-hydroxy-beta-methylbutyrate, or HMB. This is a naturally occurring compound derived from the amino acid leucine, and it has been studied specifically for its effects on lean body mass in people at risk for muscle wasting. A meta-analysis of seven randomized controlled trials found that HMB supplementation can prevent the loss of lean body mass in older adults without significantly changing fat mass.⁵

In a hospital setting, this translates to a practical difference. Research comparing standard high-protein ONS to HMB-enriched ONS found that lean body mass remained stable in the HMB group while it declined in the control group during hospitalization.⁶ For someone spending days or weeks in a hospital bed, preserving muscle mass is not a cosmetic concern. Lost muscle directly slows recovery, impairs mobility, and makes falls more likely after discharge. The HMB-enriched formulations cost slightly more per serving, but the difference is small, roughly a few extra cents per bottle.

Side Effects and Tolerance

Ensure drinks are generally well tolerated, but they are not free of side effects, particularly when someone is new to them or consuming them in larger quantities. The most common complaints are gastrointestinal: bloating, gas, nausea, diarrhea, and a general feeling of fullness that can paradoxically suppress appetite for regular food. For someone already eating poorly, having a supplement compete with meals rather than complement them can be counterproductive if timing is not managed well.

The sugar content in standard Ensure formulations is a legitimate concern for people with diabetes or insulin resistance. A regular 8-ounce bottle of Ensure Original contains around 15 grams of added sugar, and the higher-calorie versions contain more. While this is not extreme by the standards of processed food, it is enough to spike blood glucose in someone with impaired glucose control if consumed quickly on its own. Ensure does make diabetes-specific formulations with lower sugar and higher fiber, but the standard versions are the ones most commonly grabbed off the store shelf or distributed in healthcare settings.

Another less-discussed issue involves vitamin K. Ensure products contain vitamin K as part of their micronutrient profile, which can interact with blood-thinning medications like warfarin. Research has shown that warfarin bioavailability drops substantially when administered with enteral feeding formulas, with warfarin concentration falling by about 35% in some experimental setups.⁷ People taking warfarin who add Ensure to their routine, or change the amount they consume, should let their doctor know so their blood clotting levels can be monitored and the medication dose adjusted if needed.

Why People Stop Drinking Them

One of the biggest practical problems with ONS is adherence. Doctors prescribe them, patients try them, and then a significant number quietly stop. A literature review of factors affecting ONS adherence found that the main barriers are sensory in nature: the taste, aftertaste, sweetness level, and texture of the product all influence whether someone keeps drinking it.⁸ Off-flavors introduced by the protein and vitamin ingredients are a recurring complaint. Changes in taste perception that come with aging or illness can make these off-flavors more prominent.

Timing of consumption also matters. When supplements are offered between meals as a snack, adherence tends to be better than when they are offered alongside or immediately before food, since a full stomach leaves no room. Healthcare staff behavior plays a role too: if a nurse or caregiver actively encourages consumption and checks back on it, patients drink more than when the supplement is simply left on a tray. A hospital-based study found that adherence varied by flavor, with coffee and strawberry flavors outperforming others during hospital admission, possibly because extreme sweetness was less tolerable for sick patients.⁹

If you or a family member has tried Ensure and found it unpleasant, experimenting with a different flavor or serving it chilled can help. Some people blend it into a smoothie with fruit to mask the supplement taste. The clinical benefits only materialize if the product is actually consumed consistently, so finding a tolerable form matters more than choosing the theoretically optimal formula.

Gastric Emptying and Feeling Full

One property of Ensure that is clinically useful in some settings but annoying in others is how slowly it leaves the stomach. A study comparing Ensure Plus to a standard egg-based meal found that the liquid supplement and the solid meal emptied at similar rates in the first two hours, but Ensure Plus was retained significantly longer at three and four hours after ingestion.¹⁰ At the four-hour mark, roughly 9% of the Ensure Plus remained in the stomach on average.

For researchers, this makes Ensure Plus a convenient standardized meal for gastric emptying tests. For consumers, it explains why a single bottle can cause prolonged fullness, especially in people with slower-than-normal stomach motility. If you are using Ensure to increase your caloric intake but find that it kills your appetite for actual meals, this delayed emptying is probably part of the reason. Drinking smaller amounts more frequently, rather than one full bottle at once, can reduce this effect.

The Cost-Effectiveness Question

Ensure and similar ONS products are not cheap when purchased out of pocket, typically running a few dollars per bottle at retail. For someone drinking two bottles a day, monthly costs add up quickly. Whether this makes economic sense depends heavily on the context.

From a healthcare system perspective, the math favors supplementation for malnourished patients. A US-based economic model estimated that if ONS were provided to the roughly 1.7 million older patients at risk of malnutrition in the US each year, the resulting reduction in hospital readmissions could prevent about 117,000 readmissions annually and save approximately $1.9 billion in healthcare costs, even after accounting for the cost of providing the supplements.¹¹ The cost of ONS following discharge was estimated at about $175 per patient per month, or roughly $2,546 per readmission avoided.

A similar analysis in China found that ONS use in hospitalized patients was cost-effective when measured against the country’s per-capita GDP threshold, a standard benchmark for evaluating healthcare interventions.¹² Meanwhile, a study in Israel comparing standard ONS to HMB-enriched ONS found that the slightly more expensive HMB formula generated net savings of about $400 per patient over six months through reduced readmissions, despite costing only a few extra dollars over a hospital stay.¹³

These numbers come from models and retrospective analyses, not randomized cost trials, so the real-world savings will vary. But the general pattern is consistent across countries and healthcare systems: for genuinely malnourished patients, spending a modest amount on ONS avoids far more expensive hospital costs downstream.

When Ensure Is Not the Right Choice

The popularity of Ensure has pushed its use well beyond the clinical populations where it has proven value. Healthy adults with normal appetites and no medical conditions rarely benefit from adding a nutritional supplement drink to their diet. You are essentially consuming extra calories, sugar, and processed ingredients in a situation where whole food would provide the same or better nutrition. Using Ensure as a convenient breakfast replacement when you could eat actual food is a bit like taking a cast off the shelf because you like the support, even though your arm is not broken.

For athletes or people trying to gain weight, there are more efficient and less expensive ways to increase protein and calorie intake. A glass of whole milk, a handful of nuts, or a homemade smoothie with Greek yogurt and a banana will deliver similar macronutrients without the added sugar, artificial flavors, and cost premium. Ensure’s value lies in its standardized, nutrient-complete formula for people who cannot reliably get what they need from food, not in any magic ingredient unavailable through a normal diet.

People with kidney disease need to be cautious as well. Many Ensure formulations contain levels of potassium, phosphorus, and protein that can be problematic for someone with impaired kidney function. Renal-specific supplements exist for this population, but standard Ensure is not one of them. Anyone with kidney disease should talk to a dietitian before using these products.

Food-Based Alternatives for Swallowing Difficulties

For older adults with dysphagia, or difficulty swallowing, commercial formulas like Ensure are commonly prescribed because their thin or semi-thick liquid consistency is easier to manage than solid food. But food-based alternatives are gaining attention. A study comparing high-protein, low-carbohydrate smoothie formulas to commercial Ensure found that certain smoothie formulations produced fewer premature spills into the throat in people with swallowing symptoms.¹⁴ This suggests that well-designed food-based options could be both safer for swallowing and more palatable than commercial supplements, though more research is needed before they can be recommended as a standard replacement.

The broader point is that Ensure is one tool in a nutritional toolkit, not the only option. When the goal is to deliver calories and protein to someone who cannot eat normally, the best approach is whichever one the person will actually consume consistently, whether that is a commercial supplement, a carefully prepared homemade smoothie, or some combination of both. The perfect formula that sits untouched on a nightstand is worth nothing.