Registered Dietitian Analyzes Old-school Bodybuilding Diet "Tuna & Water" to get Shredded

Added: 2026-05-31

[00:00:00]All right. What's going on everyone?

[00:00:01]Seth here, registered dietician. And if you don't know what that is, that's okay. Basically, it just means I went to school for a bunch of years. I learned a lot about human physiology and biochemistry and food science. But then I spend most of my time just telling people to eat less. But speaking of eating less, there's a pretty wild diet that I found that started back in the 1970s with a guy named Dave Draper. He's a pretty famous bodybuilder. You might have heard of him called the tuna and water diet. If you never had the pleasure of hearing about the tuna and water diet or maybe even trying it, you're definitely going to want to tune into this video to see what it's all about. Now, tuna and water sounds pretty reasonable. A lot of bodybuilders eat tuna and drink water. Problem is, that's all you get for the whole contest prep.

[00:00:51]Tuna and water. Now, if you're a cat, that might not be too bad. people and especially bodybuilders might need a little bit more than that. So, let's look at some of the specifics of what this diet was all about and where it even came from. Right? So, I mentioned Dave Draper and he's the one that originally came up with this diet, but he didn't intend for it to be used for an entire contest preparation. In fact, the original plan was just for 3 days.

[00:01:18]It was meant as sort of a cleanse. Cut out the junk food, cut out the snacks, just eat clean, lean protein for two or three days, drink some water, and that would kind of kickstart your diet and get you into a nice fat loss phase. But of course, bodybuilders never do anything just straightforward as it's supposed to be. They've got to take things to the extreme. If three days of tuna and water lost a few pounds and got you feeling lean, then six or eight weeks of nothing but tuna and water has to be a lot better, right? You could just do your entire contest prep with nothing but tuna and water. You're going to be peeled to the bone. All right, so the plan called for 1.5 g of protein per pound of body weight just in tuna. So for a 200lb bodybuilder, that would be 300 g of protein coming from tuna, which comes out to about 11 5 oz cans. That's right. You've got to eat 11 cans of tuna every single day. Now, this would undoubtedly put you in a massive calorie deficit, and you would lose fat for sure. But let's talk about some of the negatives that might come along with a dietary approach like this. All right, problem number one. You're not eating any carbohydrates. And you might think, "Yes, that's what I want. I want to burn out all the carbs in my body. Then my body will be forced to use fat for energy." And that sounds nice at first.

[00:02:41]But then you have to think about the entirety of the contest prep. You're training regularly. You're doing cardio and you have to live. Most people have jobs. You have to be able to function as a human being. If you have no carbs in your body, you're also not eating any dietary fat. What will the body turn to for a fuel source? Exactly. your own muscle tissue. But it gets even worse.

[00:03:03]When your body is in a severe calorie deprivation, your pituitary gland stops producing thyroid stimulating hormone.

[00:03:11]And without TSH, your body stops producing T4 and your metabolism crashes. But even if you suffered through all of that and lost all the body fat, you would still wind up looking terrible on stage because you're totally depleted of glycogen. Glycogen being the stored form of carbohydrate in the body importantly fills up your muscle cells with water. So a depleted bodybuilder is going to look very flat on stage while a carbed up bodybuilder will look nice and full. Actually being carbed up can make you look even leaner than if you were flat. Every gram of glycogen holds 3 g of water. And if all of that wasn't enough, the FDA's safe oral dosage for mercury is 0.1 microgram per kilogram of body weight. Using the 200 lb bodybuilder example, you'd be eating about 2 lbs of tuna every day, exceeding the safe limit of mercury by about 2,200%.

[00:04:08]Even if you somehow wound up finishing the show and looking good, you might just succumb to mercury poisoning. But thankfully, not every bodybuilder of that era was crazy about this diet. In fact, Mike Mener pushed back on this diet and had this to say. Mike noted that eating nothing but tuna and water to lean out is not only physiologically unnecessary, but psychologically destructive. And I have to agree. But sadly, I see close proximities to this sort of diet still today. Usually, it takes the form of something like tilapia and broccoli for 8 weeks. A lot of coaches push cookie cutter plans on new bodybuilders. They don't know any better and they wind up dealing with a lot of these issues I discussed in this video.

[00:04:55]So, anyway, don't be one of those people if you're doing a competition prep or just trying to lose some body fat in general. You don't have to do anything extreme. You can lose weight in a perfectly reasonable and safe, healthy way. I think that wraps up this video.

[00:05:09]Let me know if you guys have ever tried any wild extreme diets like this. And if so, uh, what did you experience?