Created for Greatist by the experts at Healthline. Read more

File this under: interesting health trends taking over the internet. There’s a diet out there called the tuna diet. It’s a short-term, crash diet designed to yield rapid weight loss.

Basically, you eat tuna (and nothing else) and drink loads of water (and nothing else) for a few days.

Feeling confused? We were, too. After all, humans are not whales or sharks, so we need to eat more than just tuna to survive.

Mono diets like the tuna diet — in which you eat a single food for days or weeks at a time to lose weight — might sound simple and convenient, but they can actually cause harm, says Samantha Coogan, MS, RD, the director of the didactic program in nutrition and dietetics at the University of Nevada Las Vegas.

“Unfortunately, most [people] want that quick fix with the lowest amount of effort possible,” she says. “Removing any — or even one — major component of [a balanced diet] poses risks.”

The tuna diet goes even further, removing virtually all carbohydrates and leaving behind only protein and some fat. And given the heavy metal content of certain types of tuna, you actually risk harming your brain health if you try to follow this diet for the long haul.

Mercury poisoning is the cause of “Mad Hatter’s Disease” — named because hatmakers used to use mercury to treat felt — and ended up poisoning themselves. You’re not likely to experience this in 2020 (yay modern medicine!), but you get our point: Mercury overload is not a great idea.

The tuna diet is the invention of a bodybuilder named Dave Draper.

It’s low in calories and carbs and high in protein, and even he admits it’s not for the faint of heart. The point of the super restrictive diet is to help fellow bodybuilders shed weight fast to show off those muscle gains before a competition.

There’s not much research behind it, but the gist of it is to focus on eating protein while eliminating fat, sugar, and carbohydrates. Draper also pushes an emotional intention to the diet, which highlights practicing discipline while breaking bad habits in your diet (think of it as a “reset”).

While eating a variety of foods for satiety and pleasure every day is not a habit you need to break, it’s again worth mentioning this is a crash diet for athletes and bodybuilders prepping for competition.

And even if tuna is your favorite food in the entire world, this diet isn’t about taking pleasure in eating. It’s not like the tuna version of that scene in “Forrest Gump.”

Nope. It’s canned tuna for breakfast. Canned tuna for lunch. Canned tuna for a snack… you get the picture.

Here’s how the tuna diet works: Basically, you eat 1 to 1.5 grams of protein (in the form of plain tuna) per pound of bodyweight daily, divided into six small meals, for 3 days. You also drink 2 to 4 liters of water per day.

A 150-pound person would consume 150 to 225 grams of protein. So, about six to nine 5-ounce cans of tuna daily (that’s canned tuna, packed in water and drained). Oh, and you get to take a fiber supplement at night, too, to help prevent constipation (yay!).

After 3 days, you add back foods like vegetables, fruit, poultry and low-fat dairy, at a ratio of 40 percent protein and 30 percent each of carbs and fat. (That part’s not extreme.)

After 3 days, you add back foods like vegetables, fruit, poultry and low-fat dairy, at a ratio of 40 percent protein and 30 percent each of carbs and fat. (That part’s not extreme.)

The tuna diet is simple, so it has that going for it. You… eat tuna. And absolutely nothing else.

Here’s why the tuna diet is not sustainable — and could be downright dangerous.

Coogan says you should definitely talk to a doctor before trying the tuna diet, and she would encourage folks to “also continue to incorporate a variety of foods.”

Your brain needs carbs

While it’s fine to reduce your carb intake, says Coogan, completely eliminating this essential macronutrient from your diet is a different story.

“You could possibly impair neurological signaling, since the brain’s main source of fuel is glucose,” she cautions.

What’s the harm in that? “Undue fatigue, disorientation, lethargy, and difficulty concentrating,” says Coogan.

And, she adds, you may also deplete your stores of glycogen (stored glucose), which serves as a critically important reservoir when your blood sugar dips. (Hello, hanger!)

Your stored glycogen also affects your power output during physical activity. Without carbs, you might not have the energy to get through your workout. (Bye-bye, gains!)

You won’t get enough essential nutrients

Carbs aside, following the tuna diet means you could be missing out on some fat-soluble vitamins (including vitamin A, which is crucial for eye health) and other water-soluble vitamins and essential minerals, says Coogan.

Follow the tuna diet for too long, and you could experience side effects like night blindness, muscle wasting, or blood disorders. That’s because some nutrients “are synergistic with others and require the presence of another to enhance absorption,” she explains.

Variety isn’t just the spice of life — it’s a safer nutrition “investment strategy,” says Coogan. She compared eating a mono diet to dumping your entire life savings into a single stock.

“Think of it in terms of diversifying an investment or stock portfolio,” she says. “You don’t want to put all of your eggs in one basket (forgive the unintentional nutrition pun), but you can’t bank all of your nutrient quality on one food source.”

You could harm your metabolism

Ironically enough, the tuna diet is aimed at weight loss, but it could ultimately impair your metabolism, warns Coogan.

Since no single food can provide everything you need to stay healthy, by eating only tuna, you’re also reducing your micronutrient intake. (You are encouraged to take a multivitamin during the tuna diet, btw, but that’s not reason enough to try it.)

“You run the risk of harming your typical metabolic rate and pathways,” she says. “Micronutrients act as precursors to macronutrient metabolism, and also as co-enzymes for other metabolic reactions.”

Your metabolism likes variety

During exercise, muscle confusion “allows the body to adapt to new stimuli in order to progress,” Coogan says.

Just as you should regularly shake up your workout routine if you want to get stronger or change your body composition, you should also change up your diet for optimal metabolism.

“The digestive tract needs more than just the same thing day in and day out to keep your metabolic rate running as efficiently as possible,” she says.

“Once the body adapts, it’s very easy for the body to learn to compensate and slow down if it becomes accustomed to receiving the same thing over and over again.”

If you do decide to shift your macronutrient balance to reduce carbs and eat more protein, you have to consume more than tuna. Even eating a variety of fish (if for whatever reason you’re not consuming animal products or plant based proteins) is a better option than only tuna, says Coogan.

You can overdo it on mercury — seriously

The 2010 Dietary Guidelines for Americans recommend eating about 8 ounces of seafood per week, but you would exceed that amount in just two meals and you would get 5 to 6 times the recommended amount in 1 day on the tuna diet.

While you likely don’t need to worry about “Mad Hatter’s Disease” after 3 days of the tuna diet, mercury exposure is a legit concern if you eat too much tuna (and shark and swordfish).

A 2009 research article reads like a script from a medical drama: Two otherwise healthy middle-age men presented with mysterious pain, weakness, fatigue, and weight loss.

Eventually, doctors realized their fish-only diet was to blame. The men had low-level mercury poisoning! (They recovered.)

“Mercury poisoning can lead to irritability, numbness, depression and changes in taste perception (specifically a metal taste) — and in more severe cases neurological disorders, such as muscle tremors, paralysis, and memory loss, reproductive issues, heart attack, or coronary artery disease,” says Coogan.

The takeaway

  • The tuna diet is a crash diet that a bodybuilder developed to jump-start weight loss.
  • For 3 days, you eat 1 to 1.5 grams of protein (in the form of tuna) per pound of body weight, and you drink 2 to 4 liters of water.
  • The diet is extremely restrictive and could cause all kinds of short- and long-term side effects as well as nutrient deficiencies.
  • The tuna diet is potentially dangerous, monotonous — and stinky. Don’t try this at home, friends!