Fruits and vegetables are undoubtedly filled with lots of nutrients that contribute to good health, but following a strict fruit and vegetable diet plan that includes no other categories of foods can set you up for some potentially serious health problems.
Solely relying on fruits and vegetables for all your meals can make it difficult to meet your protein needs. Although they provide many vitamins and minerals, they're also high in carbohydrates, which can lead to other health problems when eaten in excess.
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Lack of Protein
Fruits and vegetables contain tons of vitamins and minerals, but they're both low in protein, which is an essential part of a healthy diet. Protein plays a number of important roles in your body. The macronutrient is used to:
- Create bones, cartilage, muscle, skin, hair and nails (which are made mostly of protein).
- Repair damaged tissue and build new tissue.
- Carry oxygen and vital nutrients to every cell in your body.
- Help you digest food.
- Regulate hormones (especially during times of growth, like puberty or pregnancy).
- Keep you feeling full and help you maintain your weight.
Getting enough protein every day is a vital part of making sure your body is running as it should. Without it, your body will begin to break down. One study, published in Scientific Reports in April 2016, compared no- and low-protein diets to moderate-protein diets and found that the diets with the least amount of protein increased the risk of fatty liver and muscle breakdown. Low-protein diets were also linked to increased body fat and weight gain.
Your Protein Needs
Some fruits and vegetables contain protein. For example, green peas contain 8.6 grams per cup, spinach contains 5.3 grams per cup and a cup of asparagus offers 4.3 grams. A cup of guava contains 4.2 grams of protein, while a cup of avocados and a cup of apricots contain 4.0 and 2.2 grams, respectively.
The current recommendation for protein is 0.8 grams per kilogram of body weight. That means that, if you weigh 150 pounds, you need about 55 grams per day. If you weigh 175 pounds, that number jumps to 64 grams. While you could technically meet those numbers with fruits and vegetables, it would take a huge volume that would be hard to get down in one day. To put it into perspective, if you weigh 175 pounds, you'd have to eat more than 12 cups of cooked spinach to get enough protein.
Fruits and Vegetables: Incomplete Proteins
But it's not just the amount of protein that's a concern — it's the quality. Proteins are classified as either complete or incomplete based on their amino acid profile. Your body needs a total of 20 amino acids to carry out its basic functions. Of these amino acids, 11 are considered nonessential because your body can make them on its own. The other nine are considered essential because your body can't make them and you have to get them from your diet.
Protein sources that contain all nine essential amino acids are classified as "complete" proteins, while sources that are missing some or that are low in any of the essential amino acids are deemed "incomplete" proteins. Animal foods, like meat, poultry, seafood and eggs, are complete proteins, whereas most plant-based proteins, like fruits and vegetables, are incomplete proteins.
That means that, even if you're hitting your protein quantity goals by eating a ton of servings of vegetables per day, you'll probably still be missing essential amino acids that are vital to your health. The Cleveland Clinic notes that your diet will also likely be low in vitamin B12, calcium, vitamin D, iodine and omega-3 fatty acids, as well.
Overdoing It on Fructose
But the lack of protein isn't the only problem. It's also that fruits and vegetables are high in carbohydrates. Granted, many of those carbohydrates come in the form of fiber, but a lot are also in the form of fructose, which is the main sugar in fruit.
As part of a healthy, balanced diet, the fructose you'll get from eating some fruit here and there isn't going to cause a problem; but when fructose makes up the bulk of your diet, it has the potential to lead to some serious issues. According to a study published in Nutrients in April 2017, consuming a lot of fructose over a period of several days can increase the levels of uric acid, a metabolic waste product, in your blood. Chronic high levels of uric acid are associated with metabolic syndrome, high blood pressure, heart disease, kidney disease, Type 2 diabetes and cognitive decline.
Another study, published in Digestive Diseases and Sciences in May 2016 looked specifically at the effect of fructose on your liver. Fructose is not absorbed like other sugars. Instead of entering the bloodstream via the small intestine, fructose goes straight to the liver through your portal vein. When it reaches the liver, fructose prompts a process called de novo lipogenesis, or the creation of fat from carbohydrates, which can lead to non-alcoholic fatty liver disease, insulin resistance and increased abdominal fat.
Read more: List of Foods High in Fructose
Other Problems With Excess Carbohydrates
Researchers from another study, published in Diabetes Care in April 2013, compared the effects of a high-protein diet to a high-carbohydrate diet. They put two groups of participants on separate diets. One was high in protein, but low in carbohydrates, while the other was high in carbohydrates, but low in protein, like a fruit and vegetable diet plan.
Both diets were designed to provide the same amount of calories and micronutrients. While participants in both groups lost weight, the high-protein diet improved insulin sensitivity, increased the function of the beta cells (that produce insulin) in the pancreas and increased metabolic rate, while the high-carbohydrate diet did not.
The high-protein diet also decreased markers of chronic inflammation and oxidative stress, which is the underlying cause of many chronic diseases. The high-carbohydrate diet did not.
Fruit and Vegetable Diet Plan
If you're looking for a way to improve your health, or you just want to eat more fruits and vegetables every day, there are ways to do it without following such a restrictive diet plan. Consider going plant-based, which means your diet contains a lot fruits and vegetables, as well as ample amounts of protein-rich foods like nuts, seeds and legumes and some high-quality meats and animal protein sources, like chicken, grass-fed beef, eggs, fish and dairy products.
Harvard Health Publishing notes that a plant-based diet contains all of the necessary nutrients, like protein, fats, carbohydrates, vitamins and minerals, that you need to sustain optimal health, unlike a fruit and vegetable diet plan, which can leave you lacking in protein and fat. A plant-based diet is also higher in fiber and important antioxidants and phytochemicals than diets that don't contain a lot of plant foods.
If you want to get healthier, start by eating more servings of vegetables per day, instead of following a restrictive fruit and vegetable diet plan that leaves you at risk of health problems.
- Scientific Reports: "Low Protein Diets Produce Divergent Effects on Energy Balance"
- U.S. Food and Drug Administration: "Protein"
- Cleveland Clinic: "Fruitarian Diet: Is It Safe — or Really Healthy for You?"
- Diabetes Care: "Effects of High-Protein Versus High-Carbohydrate Diets on Markers of β-Cell Function, Oxidative Stress, Lipid Peroxidation, Proinflammatory Cytokines, and Adipokines in Obese, Premenopausal Women Without Diabetes"
- Nutrients: "Fructose Intake, Serum Uric Acid, and Cardiometabolic Disorders: A Critical Review"
- Digestive Diseases and Sciences: "Role of Dietary Fructose and Hepatic de novo Lipogenesis in Fatty Liver Disease"
- MyFoodData: "Top 10 Vegetables Highest in Protein"
- MyFoodData: "Top 10 Fruits Highest in Protein"
- Harvard Health Publishing: "What Is a Plant-Based Diet and Why Should You Try It?"
- Harvard T.H. Chan School of Public Health: "Protein"
- Piedmont Healthcare: "Why Is Protein Important in Your Diet?"