Asking whether the cholesterol in a food is healthy is missing the point when it comes to dietary cholesterol. It's not the cholesterol in a food, but the ability of a food to stimulate your body's production of its own cholesterol, that's primarily responsible for your cholesterol levels. The fats and oils in canned tuna will stimulate that production.
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Your blood contains three kinds of cholesterol: LDL, HDL and triglycerides. LDL, or low-density lipoprotein, is bad for you. It clumps up in your blood stream and increases your risk of circulatory illnesses. HDL, or high-density lipoprotein, cleans the LDL out of your blood and improves your cardiovascular health. Triglycerides are unhealthy for the same reasons as LDL, but are not as harmful as LDL.
Cholesterol and Diet
What you eat has a strong effect on your cholesterol levels. Your body produces harmful LDL cholesterol when you eat saturated fats. Eating unsaturated fats stimulates your body to produce the beneficial HDL cholesterol. Triglycerides form in response to the presence of blood glucose, produced when you consume sugars and unrefined carbohydrates.
Tuna in Water
The US Department of Agriculture provides nutrition information for thousands of foods, including canned tuna. According to the USDA, tuna canned in water contains about 1.4 g of saturated fat and 3.2 g of unsaturated fat per can. Tuna canned in water contains no carbohydrates or sugars.
Tuna in Oil
According to the USDA, tuna canned in oil contains 2.6 g of saturated fat per can, and 10 g of unsaturated fats. Like tuna in water, tuna canned in oil contains neither carbohydrates nor sugars.
Although it does contain some saturated fats, canned tuna contains far more healthy unsaturated fats and should contribute to healthy cholesterol levels. However, the presence of saturated fats makes it a poor choice for people who already have dangerously high levels of cholesterol. This is especially true of tuna canned in oil.