Tuna Diet: Does It Actually Help With Weight Loss?

Tuna ranks top on the seafood list, roaming from the Atlantic to Indonesia. It’s a big hit in Asian meals and just as loved in Europe and Australia (1)(2). Anyone who enjoys a good plate of seafood will find this fish fascinating. With every bite, they’ll unlock the flavors of the ocean. So, why stop diving into the tasty world of tuna?

Tuna comes from a variety of species that are found all over the world, which includes the blue fin, yellow fin, and bullet tuna – to name a few. The most popularly known tuna species in the United States are Skipjack (also known as light tuna), and Albacore (or “white” tuna). In addition, Albacore is the only tuna that can be sold under the name “white meat tuna (1)(2).”

Overall, there are eight species of tuna – all of which are nomadic, which means that they are continuously migrating. Still, they are easily found in temperate and subtropical waters of the Atlantic Ocean, as well as the black waters and the Mediterranean Sea. From there, they are supplied to different parts of the world, especially in Japan and Australia. Given that they are persistently hunted throughout the year, they are now listed under the endangered species (2).

The fish is powered by essential nutrients like omega-3 fatty acids, magnesium, potassium, iron, vitamin A, B6, and B12 – all of which are beneficial for health (2).

The life of a tuna fish varies from three to five years, while some are found to have lived for over two decades. They are relatively easy to catch, and they also make a great dish for steaks, salads, burgers, and the like (2).

Tuna is one of the most popular types of seafood worldwide. Besides its abundance and meaty flavor, tuna is also extremely nutritious (1).

This fish boasts a good reputation as a healthy food, as it is loaded with essential nutrients that boost your overall health and well-being. The best part is that it’s great for weight loss, given its low-calorie and low-fat combinations. Plus, you won’t have to worry about being healthy, as this fish’s low-calorie varieties offer the healthiest option (3).

Tuna is a high protein food; given that it is a lean fish, it does not contain much fat. Given this, it is popular among bodybuilders and fitness models who are on a diet. If you are trying to go for protein intake, make sure you choose canned tuna in water, not oil (4).

Before starting a new diet – such as the one that we will talk about today – it’s best to consult a medical professional and visit a nutritionist or registered dietitian to help you plan your diet regimen (3).

In this article, we are going to tackle at least two main topics: tuna diet and canned tuna. Before we go deeper to the topic, let’s first emphasize the benefits of tuna, in general.

Health Benefits of Eating Tuna

Consuming fish is healthy and offers tons of benefits – from improving the eyesight and hair quality to keeping your heart healthy (2). When taken in moderation, tuna can be a healthy, low-calorie source (5).

Although it does not offer all the nutrients that your body needs, tuna maintains a good reputation for being a healthy protein that you can add for a balanced diet. In this case, tuna is not meant to be the only source of your nutrients (5).

1. Heart Friendly

Tuna contains omega-3 fatty acids, which aid in bringing balance in their blood vessels – reducing cholesterol in the arteries. That said, the heart is able to efficiently pump blood throughout the arteries and maintain good health (2).

2. Lowered Blood Pressure

Tuna is rich in potassium, which is known for lowering blood pressure. The omega-3 fatty acids combine with potassium to bring an anti-inflammatory effect to the cardiovascular system. As a result, blood pressure, as well as the risks for stroke and heart attack, is lowered (2).

3. Improved Immune System

Tuna is rich in zinc, manganese, vitamin C and selenium – all of which helps in strengthening the immune system. The said antioxidants also protect us from illnesses like cancer by combating free radicals, which are the by-products of metabolism on the cellular level (2). Moreover, its high-selenium content promotes thyroid function and offers you anti-inflammatory and antioxidant effects (5).

4. Weight Loss

Majority of the people these days face weight as a major issue. All of us enjoy eating tasty food but we also want to maintain a slim figure. For this reason, tuna offers us good taste while balancing our calories. It’s low in fat content yet rich in proteins and nutrients (2).

5. Bone Strength

Tuna contains vitamin B, which is a major component in strengthening your bones and protecting them from injuries such as fracture (2).

6. Skin Health

The vitamin B complex in the fish helps to keep your skin looking healthy. It contains a protein known as elastin, which offers a smooth tone to our skin. So, if you plan to improve your skin’s health, tuna can help you achieve that radiant skin (2).

7. Cancer Prevention

Antioxidants from the tuna meat helps fight cancer cells. Studies show that regular consumption of tuna helps to eliminate the risk of breast and kidney cancer (2).

8. Energy Boost

Tuna not only improves your metabolism rate, but it also improves your organ’s functionality – keeping you energetic, healthy, and active. Moreover, it can also help boost your immune system (2).

The Tuna Diet

The tuna diet is a short-term eating pattern that mainly includes tuna and water. Although it causes rapid weight loss, it is very restrictive and offers many extreme downsides (5).

This diet is a low-calorie, low-carb, yet high protein eating plan that is created by a bodybuilder named Dave Draper. Basically, you are meant to consume water and tuna for three days (5).

Afterwards, you can add low-fat dairy products, poultry vegetables, and fruits for an unknown period. During this stage, your macronutrient ratio should be 40 percent protein, 30 percent carbs, and 30 percent fat. Although it is promoted as a way to break bad dietary habits and encourage quick weight loss, this crash diet is not supported by research (5).

According to Samantha Coogan, MS, RD, director of the didactic program in nutrition and dietetics at the University of Nevada Las Vegas, mono diets like the tuna diet – in which you eat a single food (in this case, tuna) for days or weeks to lose weight – might seem simple and convenient, but they can actually cause harm. On that note, she says, “Unfortunately, most [people] want that quick fix with the lowest amount of effort possible. Removing any — or even one — major component of [a balanced diet] poses risks.” (6).

The diet was invented by a bodybuilder named Dave Draper. Given that it is low in calories and carbs yet high in protein, he admits that it’s not for the faint of heart. The major point of this diet is to help bodybuilders shed those extra pounds fast to show off their muscle gains before competing (6).

Although, as mentioned, it does not have much research about it, the main idea is to focus on eating protein while eliminating sugar, fat, and carbohydrates. Draper also suggests an emotional intention to the diet, which mainly highlights the practice of discipline while breaking bad habits in your diet (6).

It’s worth mentioning that eating various foods for pleasure and satiety on a daily basis is not a habit that you need to break, and this diet was intended for athletes and bodybuilders who are preparing for a competition (6).

How It Works

Basically, you only eat tuna and drink loads of water – and nothing else – for three consecutive days (5). This diet even goes further by removing virtually all carbohydrates and leaving behind only protein and fat (6).

The tuna should be plain, which means that it is without oil, vinegar, mayonnaise, or spices, and it should be enough to provide you 1.5 grams of protein per kilogram (or 3.3 grams per pound) everyday. Divide it into six meals, for three days (5)(6). Along with this, you drink 2 to 4 liters of water each day (6).

For instance, a 150-pound person would consume 150 to 225 grams of protein. Thus, about six to nine 5-ounce canned tuna daily – packed in water and drained. Plus, you may also take in fiber supplements at night to prevent constipation (6).

After the 3-day period, you can add back foods like fruits, leafy green and steamed non-starchy vegetables, low-fat dairy, and poultry, at a ratio of 40 percent protein and 30 percent carbs and fat (5)(6).

Although there is no set duration, you are likely meant to follow it until you reach your target weight. Afterwards, you repeat it from time to time to achieve rapid weight loss (5).

Does It Help With Weight Loss?

Given that it is a restrictive diet plan, it can cause rapid weight loss due to its low calorie count. However, diets that severely restrict calories can cause harm to your health (5).

On a more serious note, severe calorie restriction slows your metabolism and impairs muscle mass. Several studies show that regularly eating far less than what your body needs lessened the number of calories that your body burns while you are at rest (5).

Moreover, severe calorie restriction triggers severe hunger, and even results in weight gain after you stop the diet (5). Overall, research suggests that very-low calorie diets like the tuna diet does not sustain well and fails to improve your body composition (5).

Risks

Given the heavy metal content of some specific types of tuna, you can actually risk harming your brain health if you try to follow this diet for a long time (6).

Mad Hatter’s Disease – coined from the hatmakers who used to use mercury to treat felt and ended up poisoning themselves – is caused by mercury poisoning. Although 2020 has introduced modern medicine to treat this, it does not eradicate the thought that mercury overload is dangerous and is not a great idea for a diet (6).

Apart from the low-calorie count, highly restrictive nature, and risk for mercury poisoning, the diet also comes with several downsides, which include (5):

1. Not Enough Calories

The tuna diet does not provide most adults enough calories. Three ounces (or 85 grams) of tuna packed in water contains 73 calories, 16.5 grams of protein, 0.6 grams of fat, and no carbs (5).

Thus, a 150-pound person would need 102 grams of protein daily on this diet, which is equivalent to 18.5 ounces (or 524 grams) of tuna each day – equivalent to 610 calories daily and substantially below 2,000 calories that your body needs (5).

Given this calorie restriction, you’ll have slower metabolism, loss of muscle mass, inadequate nutrient intake, extreme hunger (5).

2. Possibility for Mercury Poisoning

Despite the health benefits that tuna has, it does come with potential heavy metal poisoning.  According to the Environmental Protection Agency (EPA), one should limit their intake of canned light or skipjack tuna to 12 ounces (340 grams) weekly (5).

One should take note that not all tuna varieties can be consumed due to their high levels of mercury. This includes albacore, yellowfin, and bigeye (5).

Keep in mind that a 150-pound (68-kg) person on this type of diet would need to eat 18.5 ounces (524 grams) of tun each day, which is the same as 55.5 ounces (or 1.6 kg) over a 3-day period (5).

The maximum safe dose for mercury is 0.045 mcg of mercury per pound of body weight (or 0.1 mcg per kg), which means that a 150-pound (68-kg) person can consume up to 6.8 mcg of mercury every day (5).

However, you can easily exceed your mercury limits given that the tuna diet may contain too much of this fish (5).

Even just by eating light tuna alone, a 150-pound 968-kg) person could take in 68 mcg of mercury daily, which is 10 times the recommended amount (5). Mercury poisoning is associated with severe damage to your kidneys, heart, immune system, and nervous system (5).

3. Highly Restrictive and Short Term

It is a well-known fact that the tuna diet is very restrictive when it comes to food choices and nutrients. Given that its first phase is only meant to be applied for three days, it may not be a good diet if one is opting for a change in lifestyle and habits for long-term weight loss (5).

As a matter of fact, studies show that it’s difficult to apply fad diets like the tuna diet, as its long-term benefits are questionable. Simply put, short-term weight loss may be unsustainable and can inhibit long-term success (5).

4. Inadequate Nutrients

The tuna diet provides other downsides that may not make it sufficient to meet your nutrient needs. Sometimes, this type of eating patterns may not put into mind individual differences (5).

More notably, this diet is not backed by any study and is not realistic and safe to follow for any duration due to its restrictions and high-mercury content (5).

Following this diet could mean that you can potentially be missing out on some fat-soluble vitamins like Vitamin A, and other water-soluble vitamins and essential minerals. More importantly, following the tuna diet for too long can make you experience side effects, such as night blindness, blood disorders, and muscle wasting (6).

Coogan explains that some nutrients are “synergistic with others and require the presence of another to enhance absorption.” She adds that variety is not just the spice of life. In fact, it’s a safer nutrition “investment strategy.” Thus, Coogan compared eating a mono diet to placing your entire life savings into a single stock (6).

She further explains, “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 (6).”

All that said, the weight loss effects of this diet are more likely unsustainable (5).

5. Lacks Carbs

While it’s difficult to reduce your carb intake, completely eliminating this essential macronutrient from diet poses a great threat to your health (6).

Coogan warns, “You could possibly impair neurological signaling, since the brain’s main source of fuel is glucose.” As a result, you may experience undue fatigue, disorientation, difficulty concentrating, and lethargy (6).

She further explains that you may also lessen your glycogen storage, which is a critically important reservoir when your blood sugar decreases. Glycogen can also affect your power output during physical activity. Without carbs, you might not have the energy to get through your workout (6).

6. Harms Metabolism

Although the tuna diet is initially intended for weight loss, it can ultimately impair your metabolism. The truth is that there is no single food that can provide all that you need to stay healthy. By eating tun, you are also reducing your micronutrient intake (6).

Coogan explains, “You run the risk of harming your typical metabolic rate and pathways. Micronutrients act as precursors to macronutrient metabolism, and also as co-enzymes for other metabolic reactions (6).”

As you engage in your workout routine more often, you need to change your body composition and change your diet for optimal metabolism (6).

“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. 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.” Simply put, your metabolism thrives in variety (6).

If you decide to shift your macronutrient balance to lessen carbs and eat more protein, you can consume more than tuna. That said, eating a variety of fish is a better option than solely eating tuna (6).

The Takeaway

Although a tuna diet results in rapid weight loss, it’s not sustainable and not a good fit as a long-term solution for your weight loss goals. It is also accompanied by several risks, which includes loss of muscle mass, mercury poisoning, and slowed metabolism (6).

If you want to achieve excellent results, the best option is to adhere to a balanced meal plan that provides you with enough calories for your needs. Also, consume plenty of whole, unprocessed foods, and embark on diet and lifestyle changes that support your weight goals (6).

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