I was a Corpsman (not a corpse-man as some recent somewhat fanatical president would say), and I can tell you many stories of Marines and Sailors who maintained restrictive diets (aka picky eaters). Most obvious was lack of sustaining energy (hypoglycemia) at mile 15 (with 80lbs of gear including a 6.5lb rifle and 200 rnds of ammo, etc.) and depletion of essential vitamins, electrolyte imbalance. They were always the first to collapse and have to hear me scold “see I told you so.” An IV of D5W usually does the trick (D is for dextrose, OMG!)
Ketones—the molecules produced during fat metabolism on the keto diet and other very low-carb diets—are acidic. “When they start to build up in our blood, the blood becomes more acidic,” Notte says. One of the ways the body balances high acid levels is by using a base like calcium, she explains. “The body pulls this alkaline mineral from our bones.” In the long term, chronic calcium loss can lead to low bone density, osteoporosis, and fractures. Try these 15 ways to boost bone health.
A ketogenic diet could be an interesting alternative to treat certain conditions, and may accelerate weight loss. But it is hard to follow and it can be heavy on red meat and other fatty, processed, and salty foods that are notoriously unhealthy. We also do not know much about its long-term effects, probably because it’s so hard to stick with that people can’t eat this way for a long time. It is also important to remember that “yo-yo diets” that lead to rapid weight loss fluctuation are associated with increased mortality. Instead of engaging in the next popular diet that would last only a few weeks to months (for most people that includes a ketogenic diet), try to embrace change that is sustainable over the long term. A balanced, unprocessed diet, rich in very colorful fruits and vegetables, lean meats, fish, whole grains, nuts, seeds, olive oil, and lots of water seems to have the best evidence for a long, healthier, vibrant life.

As far as keto's track record with longer term weight loss, a systematic review and meta-analysis that looked at 13 randomized trials that lasted at least a year showed that people who followed the ketogenic diet recommendations lost, on average, 2 more pounds compared to those who followed lowfat ones. But some experts say that weight loss from a keto diet probably isn't from any specifics about the diet itself. If the ketogenic diet aids weight loss, says Brian St. Pierre, R.D., director of performance nutrition at Precision Nutrition, it’s because it might enable some people to maintain a caloric deficit.
One downside to a ketogenic diet for weight loss is the difficulty maintaining it. “Studies show that weight loss results from being on a low-carb diet for more than 12 months tend to be the same as being on a normal, healthy diet,” says Mattinson. While you may be eating more satiating fats (like peanut butter, regular butter, or avocado), you’re also way more limited in what’s allowed on the diet, which can make everyday situations, like eating dinner with family or going out with friends, far more difficult. Because people often find it tough to sustain, it’s easy to rely on it as a short-term diet rather than a long-term lifestyle.
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