Month: October 2022

Driving along the freeway recently, a billboard caught my eye. In bold letters it proclaimed:

Milk hydrates better than water.

Wait, could this be true? And if so, should I be rehydrating with milk after a workout? And should we all have milk, rather than water, in our water bottles?

What’s behind the claim?

Unsurprisingly, the ad is sponsored by the milk industry. And while I’d never heard this claim before, the studies behind the idea aren’t particularly new or compelling. The website supporting this ad cites three small studies dating back more than a decade:

• A 2007 study enrolled 11 volunteers (five men, six women) who exercised until they were markedly dehydrated on several occasions. Each time they rehydrated with a different drink, and their urine output was measured over the following five hours. After drinking milk, the study volunteers produced less urine (and therefore retained more fluid) than with water or a sports drink (Powerade). Therefore, milk was considered to provide better hydration.
• A study published in 2016 described seven men with marked dehydration following exercise who drank fat-free milk, water, or Powerade. The results were similar.
• A 2016 study enrolled 72 healthy, well-hydrated men who drank various fluids and then had their urine production measured over the next four hours. The drinks used in this study were water, whole milk, skim milk, beer, Dioralyte (an oral rehydration solution used after fluid loss from diarrhea), tea, coffee, diet cola, regular cola, orange juice, and Powerade. The researchers found that fluid retention was best after drinking either type of milk or the oral rehydration solution; results for the other drinks were similar to water.

Sounds like milk is a winner, right? Maybe. But there are other things to consider.

The study details matter

The findings of these studies aren’t definitive. As with all research, there are important limitations. For example:

• The small number of participants in these studies means that just a few people could have an outsized impact on the results.
• Two of the three studies involved significant dehydration by intensely exercising in a warm environment, leading to several pounds of fluid loss. Therefore, the results may not apply to people engaged in more typical daily activities or workouts. In addition, the studies equated better hydration with less urine production in the hours after drinking various fluids. This is only one way to define hydration, and not clearly the best one.
• The advantage of milk reported in these studies may be too small or too temporary to matter much. For example, in the study of 72 people, milk drinkers produced about 37 ounces of urine over four hours while water drinkers produced 47 ounces. Does the 10-ounce difference have a meaningful health impact? If the study participants had been monitored for a longer period, would this difference disappear?
• The amount of milk consumed in the study of seven men would contain more than 1,000 calories. That may be acceptable for an elite athlete after hours of intensive exercise in the heat, but counterproductive and costly for someone working out for 30 minutes to help maintain or lose weight. Tap water is free and has no calories!

Hyping hydration: Many claims, little evidence

The billboard promoting milk reflects our relatively recent focus on hydration for health. This is promoted — or perhaps created — by advertisers selling sports drinks, energy drinks and, yes, water bottles. But does drinking “plenty of water” translate to weight loss, athletic performance, and glowing appearance? Does monitoring urine color (darker could indicate dehydration) and downing the oft-recommended eight glasses of water daily make a difference in our health? On the strength of evidence offered so far, I’m not convinced.

But wait, there’s more! Emotional support water bottles, a trend popularized recently in Australia, offer one part public expression of your commitment to health and one part security blanket. (Yes, it’s a thing: #emotionalsupportwaterbottle has more than 80 million views on TikTok.) And then there’s intravenous hydration on demand for healthy (and often wealthy) people convinced that intravenous fluids will improve their looks, relieve their hangovers, help with jet lag, or remedy and prevent an assortment of other ailments.

Is this focus on hydration actually helpful?

Before water bottles were everywhere and monitoring fluid intake became commonplace, medically important dehydration wasn’t a problem for most healthy people who were not rapidly losing fluids due to heat, intense exercise, diarrhea, or the like.

The fact is, drinking when thirsty is a sound strategy for most of us. And while there are important exceptions noted below, you probably don’t need fluids at hand at all times or to closely monitor daily fluid intake to be healthy. There are far more important health concerns than whether you drink eight glasses of water each day.

When is dehydration a serious problem?

Weather, exercise, or illness can make dehydration a major problem. Particularly susceptible are people who work or exercise outside in hot and humid environments, those at the extremes of age, people experiencing significant fluid loss (as with a diarrheal illness), and those without reliable access to fluids. If significant dehydration occurs, replacing lost fluids is critically important, and may even require a medical setting where intravenous fluids can be provided quickly.

The bottom line

Despite the claims of milk ads and the iffy studies justifying them, the idea of replacing water with milk for rehydration may not convince everyone: the taste, consistency, and extra calories of milk may be hard to get past.

As for me, until there’s more convincing evidence of an actual health advantage of milk over water for routine hydration, I’ll stick with water. But I’ll forego the water bottle.

Follow me on Twitter @RobShmerling

About the Author

Robert H. Shmerling, MD,

Senior Faculty Editor, Harvard Health Publishing; Editorial Advisory Board Member, Harvard Health Publishing

Dr. Robert H. Shmerling is the former clinical chief of the division of rheumatology at Beth Israel Deaconess Medical Center (BIDMC), and is a current member of the corresponding faculty in medicine at Harvard Medical School. … See Full Bio View all posts by Robert H. Shmerling, MD

Understandably, the sensitive topic of weight in children and teens often focuses on the health costs of overweight and obesity. Sometimes, though, a child needs to gain some weight. And while there are lots of ways to make that happen, not all of them are healthy.

What to do if your child seems underweight

If you are worried about whether your child needs to gain weight, it’s very important to check with your doctor before getting to work on fattening them up. It’s entirely possible that your child’s weight is absolutely fine. Given that one in five children in the US is obese and another one in six is overweight, it’s easy to see how a parent might think their child is too thin in comparison. One way to find out if your child’s weight is healthy is to check their body mass index, a calculation using height and weight that is used for children ages 2 and up.

Losing weight or being underweight can be a sign of a medical or emotional problem, so be sure to let your doctor know about your concerns. They may want to see your child to help decide if any evaluations are needed. If your child is less than 2 years old, it’s particularly important that you check in with your doctor about weight concerns, and follow their advice exactly.

Choosing healthy foods when a child needs to gain weight

If your child is older than 2 and the doctor agrees that gaining weight is a good idea, the best way to approach it is by using healthy foods and healthy habits.

Three ways to help encourage healthy weight gain:

• Give your child three meals (breakfast, lunch, and dinner) and two healthy snacks (mid-morning and mid-afternoon). If your child eats dinner early, you could consider a small snack before bedtime. Try to avoid snacks in between or drinking anything other than some water; you want them to be hungry when you give them food.
• Offer healthy high-calorie foods. Think in terms of healthy fats and protein. Some examples are:
  • nuts and nut butters, as well as seeds like pumpkin or sunflower seeds
  • full-fat dairy, such as whole milk, heavy cream, cream cheese, and other cheeses
  • avocados
  • hummus
  • olive oil and other vegetable oils
  • whole grains, such as whole-wheat bread or granola (look for granola sweetened with juice or fruit rather than sugar)
  • meat if your diet includes it
• Every time you prepare a meal or snack, think about how you might add some calories to it. For example, you could add some extra oil, butter, or cheese to pasta — or some nut butter on a slice of apple or piece of toast.

Three traps to avoid:

• Giving your child more sweets or junk food. It’s tempting, as children generally want to eat sweets and junk food, and both have calories. But they aren’t healthy foods, and it’s not a good idea to build a sweets and junk food habit.
• Giving your child unlimited access to food. This, too, is tempting — after all, you want them to eat! But not only does that make it hard to be sure that what they are eating is healthy, snacking can make them less hungry when it’s time for an actual meal.
• Letting your child fill up on milk and other drinks — including nutritional supplement drinks. This, too, makes it less likely that they will eat at mealtime, and they are unlikely to get all the nutrients they need. Don’t give your child nutritional supplements unless your doctor advises you to do so.

Be sure you schedule regular check-ins with your doctor to monitor your child’s progress. Hopefully your child will soon be at a healthier weight that helps them to thrive as they grow.

Follow me on Twitter @drClaire

About the Author

Claire McCarthy, MD, Senior Faculty Editor, Harvard Health Publishing

Claire McCarthy, MD, is a primary care pediatrician at Boston Children’s Hospital, and an assistant professor of pediatrics at Harvard Medical School. In addition to being a senior faculty editor for Harvard Health Publishing, Dr. McCarthy … See Full Bio View all posts by Claire McCarthy, MD