9 Diet Myths, Busted: What the Science Really Says

by | Oct 19, 2026

9 diet myths busted by science, from Benchmark Nutrition

The short answer

Most diet rules you hear are either wrong or matter much less than people think. A 2026 review in the Journal of the International Society of Sports Nutrition looked at 16 common diet questions. The same three things kept winning: how much you eat overall, getting enough protein, and picking a plan you can actually stick with.

If you’ve ever stared at a banana at 9 p.m. wondering if it will “turn into fat” overnight, this post is for you. (Spoiler: the banana doesn’t know what time it is.)

Below, we break down each myth, explain what the research shows, and give you real numbers you can use. Where it helps, we list amounts in both grams per pound (g/lb) and grams per kilogram (g/kg) of body weight. To convert, 1 kg is about 2.2 lb.

Myth 1: “Eating late at night makes you fat”

The truth: Your body doesn’t have a kitchen that closes at 7 p.m. What matters most is how much you eat over the whole day, not the time on the clock.

This myth comes from two places. People who eat most of their food late at night do tend to weigh more, but that’s often because big late meals are easy to overdo. A large meal (more than 500 calories) at night also tends to fill you up less than the same meal earlier in the day. The other idea is that your metabolism “shuts off” while you sleep. It doesn’t. Your resting metabolism, which burns about 60–75% of your daily calories, keeps running all night.

In fact, a small protein snack before bed may help:

  • In one study, about 30 g of protein 30 minutes before bed slightly raised next-morning metabolism (about 100 extra calories). Not every study found this.
  • Studies found that a bedtime protein snack did not slow fat burning overnight.
  • People lifting weights for 12 weeks who added a nightly protein snack (27.5 g protein) gained more muscle and strength, with no extra fat gain.

Our recommendation: If you’re hungry at night or train in the evening, a protein-focused snack is a smart choice. Aim for about 100–300 calories with 30–40 g of protein. Greek yogurt, cottage cheese, or a casein protein shake all work. A sleeve of cookies, sadly, does not count as a protein snack.

Myth 2: “Carbs make you fat”

The truth: Eating more calories than you burn adds fat, whether those calories come from carbs or fat. Neither one is “fattening” on its own.

Carbs have had a rough few decades. In the 1980s, fat was the bad guy, so food companies pulled fat out of products and replaced it with sugar. Then low-carb diets like Atkins and keto came along, and carbs became the villain instead. Bread has been in witness protection ever since.

Here’s what the research shows:

  • Insulin isn’t the whole story. Carbs raise insulin, and insulin does help store energy. But in a tightly controlled study, cutting fat led to slightly more body fat loss than cutting the same number of calories from carbs, even though only the low-carb diet lowered insulin.
  • Long-term results are the same. A review of 61 studies with nearly 7,000 adults compared low-carb diets (under 50 g a day) with balanced diets. Weight loss was about the same, over months and over years, with or without type 2 diabetes.
  • Fat has more than twice the calories. Carbs and protein have 4 calories per gram. Fat has 9.

The real problem is ultra-processed foods that are high in both refined carbs and fat: chips, pastries, fast food. They’re easy to overeat and don’t keep you full.

Our recommendation: Don’t fear carbs. Pick mostly high-fiber sources like fruit, potatoes, oats, beans, rice, and whole grains. If you train hard, carbs are your main fuel (see Myth 7 for amounts).

Myth 3: “Fasting is the best way to lose weight”

The truth: Intermittent fasting and eating a little less each day work about the same. The best one is the one you’ll actually keep doing.

First, some quick terms:

  • Intermittent fasting (IF) means fasting for set periods of 48 hours or less. Examples are time-restricted eating (like eating only between noon and 8 p.m.) and alternate-day fasting.
  • Daily calorie cutting means eating a set amount less every day, such as 250–500 calories under what you burn.

IF doesn’t set a calorie target. The idea is that a shorter eating window leads you to eat less.

What the studies show:

  • Over about 6 months, IF led to roughly 2 lb (0.94 kg) more weight loss than daily calorie cutting. That’s real, but small.
  • After 6 months, the gap mostly closes and both groups end up in about the same place.
  • IF may help a bit more with fat loss, waist size, and blood sugar control (insulin sensitivity). Daily calorie cutting did slightly better at lowering blood pressure in one large review.

Do women need different fasting rules than men?

Not based on current research. Some short studies found that men and women burn fat a little differently during a fast. But long-term studies haven’t shown that fasting works better or worse for one sex. One 12-week study of fasting plus weight training found men lost more weight while women gained more lean muscle.

Our recommendation: If skipping breakfast makes your day easier, IF is a fine tool. If it makes you “hangry” by 10 a.m. and leads to a drive-thru by noon, eat breakfast and trim calories a different way. Both methods work when you stick with them.

Myth 4: “Eating lots of protein hurts your kidneys”

The truth: For healthy people, research hasn’t found that high-protein diets damage the kidneys.

This is one of the most stubborn nutrition myths around. It has survived longer than most gym memberships. Here’s what the research shows:

  • A review of 28 randomized studies with 1,358 healthy adults compared high-protein diets (at least 1.5 g/kg, or 0.68 g/lb, a day) with normal-protein diets. It found no harm to kidney function.
  • Weightlifters eating about 2.5–3.3 g/kg (1.1–1.5 g/lb) a day for a full year showed no harm on kidney blood tests.
  • In studies of bodybuilders and other trained athletes, protein intakes under 2.8 g/kg (1.3 g/lb) a day did not hurt kidney function.
  • An expert panel in Australia and New Zealand found no published evidence that up to 2.8 g/kg a day harms the kidneys of healthy adults.

High protein does make the kidneys filter a bit faster. Researchers see this as a normal adjustment, like your heart beating faster during a workout, not as damage.

Important: This applies to people with healthy kidneys. If you have kidney disease or reduced kidney function, follow the protein plan your doctor or dietitian gives you.

Myth 5: “Vegans can’t get enough protein”

The truth: They can, but it takes a little more planning.

Vegans do tend to eat less protein. In one large study, vegans averaged about 0.99 g/kg (0.45 g/lb) a day. Meat eaters averaged 1.28 g/kg (0.58 g/lb). That’s enough for most inactive adults, but often short for people who train.

Two things make plant protein a bit trickier:

  • Digestibility: Soy and wheat protein are absorbed about as well as animal protein (over 95%). Many other plant proteins are absorbed less well, about 50–80%.
  • Amino acids: Single plant foods are often low in one or more essential amino acids, including leucine, which helps trigger muscle building.

The fix is simple: eat more total protein, from a mix of sources.

Our recommendation for vegans who train:

  • Aim near the top of the protein range in Myth 7, since plant protein is often absorbed less well.
  • Mix sources across the day: beans with rice, tofu, tempeh, edamame, lentils, seitan, and nuts and seeds.
  • A soy or pea-and-rice protein powder makes hitting your number much easier.
  • Keep an eye on vitamin B12 (you’ll need a supplement or fortified foods), plus iron and zinc.

Myth 6: “Eating 6 small meals a day burns more fat”

The truth: The number of meals doesn’t change fat loss much. Your total food for the day does.

You’ve probably heard that small, frequent meals “stoke your metabolic fire.” It’s a great slogan. Your metabolism, unfortunately, is not a campfire.

Early studies that supported this idea only looked at people’s habits; they didn’t test meal frequency directly. When researchers did test it:

  • People cutting 700 calories a day lost the same weight and fat on 2 meals or 6 meals over 8 weeks.
  • A crossover study comparing 2 and 6 meals a day on the same calories found no difference in weight, body composition, or blood markers.

More frequent meals may still help some people. They can make hunger easier to manage, help some people stick to a calorie target, and cause less stomach discomfort. Some studies also link them to better cholesterol and blood sugar control.

Our recommendation: Eat the number of meals that fits your schedule and keeps hunger in check. For active people, 3–5 meals or snacks with 20–40 g of protein each is an easy way to spread protein through the day.

Myth 7: “There’s one perfect mix of carbs, fat, and protein”

The truth: There isn’t one magic ratio like 40/30/30. The research points to total calories, enough protein, and food quality instead.

Large reviews found that the percentage of calories from carbs, fat, or protein didn’t predict long-term weight change. Diets rich in fiber, whole grains, fruit, and dairy were linked to less weight gain. Diets heavy in refined grains, sugar, and processed meat were linked to more. In other words, what you eat matters more than hitting a perfect pie chart.

Percentages can also backfire. Take a 154 lb (70 kg) person eating 1,600 calories a day with 15% from protein. That’s only 60 g of protein, far below the 98 g minimum recommended for active people at that weight. That’s why we set protein by body weight, not by percentage.

Protein: set it by body weight

Who g per lb per day g per kg per day
Minimum for inactive adults (RDA) 0.36 0.8
Adults over 65, to protect muscle 0.45–0.68 1.0–1.5
Active adults building or keeping muscle 0.64–0.91 1.4–2.0
Lean, trained lifters cutting calories 1.0–1.4 2.3–3.1

Spread it out: about 20–40 g of protein per meal (roughly 0.11 g/lb or 0.25 g/kg). Some research suggests that trained lifters going above 1.36 g/lb (3.0 g/kg) may lose a bit more fat.

Carbs: match them to your training

Training load g per lb per day g per kg per day
Light, low-intensity activity 1.4–2.3 3–5
Moderate training (about 1 hour a day) 2.3–3.2 5–7
Hard training (1–3 hours a day) 2.7–4.5 6–10
Very hard training (4–5+ hours a day) 3.6–5.5 8–12

Fat: fill in the rest

Most active people do well with fat at 20–35% of calories, which works out to roughly 0.45 g/lb (1.0 g/kg) a day. Going much lower can make it hard to get enough fat-soluble vitamins. Lean toward unsaturated fats like olive oil, nuts, avocado, and fish.

Our recommendation: Set protein first, then carbs for your training, then let fat fill in the rest. These ranges are starting points. Your best numbers depend on your size, sport, schedule, and goals, which is exactly what a Sports Dietitian can help you dial in.

Myth 8: “A DNA test can tell you the best diet for you”

The truth: So far, there’s no proof that DNA-based diets work better than regular healthy eating.

The idea sounds great: spit in a tube, and your genes tell you whether you’re a “carb person” or a “fat person.” It’s true that people respond differently to the same diet. When calories and protein are matched, high-carb and low-carb diets give about the same average weight loss, but individuals vary a lot.

Researchers tested the DNA idea directly. They sorted 122 adults with overweight or obesity into “fat-responders” and “carb-responders” based on their genes. Then they put people on a diet that either matched or didn’t match their genes. Everyone ate 750 calories a day below their needs for 12 weeks. Matching the diet to their genes didn’t help them lose more weight.

Our recommendation: Save your money. A plan built around foods you like, enough protein, and a calorie target you can live with will beat a gene report. Your DNA can’t tell you that you’ll never eat that kale salad.

Myth 9: “Superfoods have magic powers”

The truth: “Superfood” is a marketing word, not a science word. It usually just means a healthy, nutrient-packed food.

The term started as part of advertising campaigns, and there’s still no official scientific definition. Plenty of so-called superfoods are genuinely good for you. A few even have some sports research behind them:

  • Beets: Their natural nitrates may help your muscles use oxygen more efficiently during endurance exercise.
  • Tart cherries: May reduce muscle soreness and help recovery.
  • Salmon and chia seeds: Omega-3 fats that support recovery.
  • Spinach and quinoa: Good sources of iron and magnesium.
  • Blueberries: Packed with antioxidants, but the evidence for better performance or recovery is weak. One study found faster strength recovery with a blueberry smoothie.

The catch: many of these benefits come from studies using concentrated extracts or juices, not a normal serving of the whole food. A handful of blueberries is great, but it won’t undo a weekend of pizza and no sleep.

Our recommendation: Skip the hunt for one hero food. Eat a wide variety of fruits, vegetables, whole grains, beans, nuts, and fish. A diet full of nutrient-dense foods is the real “superfood.”

Bonus round: 5 more questions the review answered

Do you need to eat extra calories to build muscle?

It helps, but how much depends on your experience. Beginners and intermediate lifters can often build muscle and lose fat at the same time without eating extra on purpose. As you get leaner and more experienced, a planned surplus matters more.

  • How much extra: about 10–20% above maintenance, or roughly 250–500 calories a day. Stay near 10% if you want to limit fat gain.
  • Who benefits most: men around the mid-teens in body fat or lower, and women around the mid-20s or lower.
  • Make the extra calories mostly protein. In studies of trained lifters, adding 400–800 calories a day of protein (up to about 2.0 g/lb, or 4.4 g/kg) did not add body fat. In one study, the higher-protein group even lost more fat.

One caution from the research: in a study where people ate far more than planned and cut back their training, the extra calories mostly turned into fat. A surplus works best with hard training.

Can you lose fat without counting calories?

Yes, by changing what you eat, which often lowers how much you eat without trying.

  • Eat more protein. A review of 24 studies with 1,063 people compared higher-protein diets (0.49–0.73 g/lb, or 1.07–1.60 g/kg) with lower-protein diets. The higher-protein groups lost about 2 lb more weight and 2 lb more fat, and kept slightly more muscle. Protein keeps you full and takes more energy to digest.
  • Cut back on carbs or fat, not both. People eating a high-protein, lower-carb diet without counting calories lost 8.9 kg (about 20 lb), compared with 5.1 kg (about 11 lb) on a high-carb diet. A low-fat diet built on fiber-rich carbs also led to weight loss without counting.

A calorie deficit is still what drives fat loss. These changes just make the deficit easier to create.

What about the carnivore diet?

There’s very little strong research on it yet. Most of what exists is surveys and personal stories.

  • A survey of 2,029 people on a carnivore diet found high satisfaction, but there was no comparison group and 63% were taking supplements.
  • Carnivore meal plans in one study fell short on thiamin, magnesium, calcium, vitamin C, and especially fiber (under 1% of the recommended amount).
  • LDL (“bad”) cholesterol tends to rise. One report found a big jump in coronary artery calcium, a sign of plaque in the heart’s arteries.

It’s also unclear whether any benefits come from the meat or simply from cutting out junk food. Even the famous 1930s Arctic explorers who ate only meat ate liver, kidney, and bone marrow, not just ribeyes.

Can athletes get everything they need from food alone?

In theory, yes. In real life, most don’t. Studies show many athletes miss their targets for calories, carbs, and protein. A study of 553 Dutch athletes found that every one of them got less vitamin D from their diet than recommended, even those taking supplements. Many women athletes were also short on iron. Creatine is another example: the amounts used in research are hard to get from food alone.

Our recommendation: Food first, then fill specific gaps with supplements. Choose products that are third-party tested, especially if you compete in drug-tested sports.

Is there one best diet for living longer?

No single “anti-aging diet” wins, but the healthiest long-lived groups share a few habits:

  • Mostly whole, minimally processed foods, like the Mediterranean diet’s fruits, vegetables, whole grains, beans, nuts, fish, and olive oil.
  • Not overeating.
  • Enough protein to protect muscle as you age: about 0.45–0.68 g/lb (1.0–1.5 g/kg) a day for older adults, with about 25–30 g per meal.
  • Lifting weights, which helps that protein do its job.
  • Friends and community, which also matter for a long life.

The bottom line

After looking at 16 of the most common diet questions, the research keeps landing on the same three things:

  1. Eat the right amount of food for your goal, whether that’s a small deficit, maintenance, or a small surplus.
  2. Get enough protein every day, set by your body weight, not a percentage.
  3. Pick a plan you can stick with. Fasting or not, three meals or six, more carbs or more fat: the best plan is the one you’ll still follow in six months.

Everything else, like meal timing, superfoods, and DNA tests, is fine-tuning at best.

Need help turning these numbers into a plan that fits your life, sport, or schedule? Send us a message. Our Sports Dietitian works with clients virtually and in person, by appointment.

Frequently asked questions

Is it bad to eat before bed?

No. Your total food for the day matters more than timing. A protein-focused snack of 100–300 calories and 30–40 g of protein before bed can even help muscle recovery.

How much protein do I need a day?

Most active adults do well with 0.64–0.91 g per pound (1.4–2.0 g/kg) of body weight a day. Inactive adults need at least 0.36 g per pound (0.8 g/kg). Adults over 65 should aim for about 0.45–0.68 g per pound (1.0–1.5 g/kg).

Is intermittent fasting better than counting calories?

Not by much. Fasting led to about 2 lb more weight loss over 6 months, and the difference mostly disappears after that. Choose the approach you can keep doing.

Will a high-protein diet hurt my kidneys?

Not if your kidneys are healthy. Studies of up to 1.3 g per pound (2.8 g/kg) a day found no harm. If you have kidney disease, follow your doctor’s guidance.

This article is for general education and isn’t medical advice. Talk with a qualified healthcare provider about your specific needs.

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