I’m a Harvard-trained oncologist: Don’t believe these 6 nutrition lies

If you want to live longer and feel better, stop chasing food fads.

Every few months, a new “miracle” plan — keto, intermittent fasting, carnivore, raw — promises to fix everything. Most don’t. Even those that show modest benefits rarely deliver results worth the time, effort, and mental energy they demand.

As a Harvard-trained oncologist and world leader in health policy, I’ve spent decades researching what actually improves health outcomes. The answer to a longer life is so simple: Good nutrition is about building habits you can sustain for years, not weeks.

While you should consult your physician before changing your diet, as individual needs vary, here are six nutrition myths I wish more people would let go of.

1. All snacking is bad

The average adult consumes nearly 500 calories a day from snacks, much of it from ultra-processed foods like chips, cookies and packaged desserts. These foods are engineered to encourage overeating.

In one study, participants eating ultra-processed foods consumed more calories and gained two pounds in just two weeks compared with those eating whole foods, even when calories were matched. These foods are also linked to higher all-cause mortality.

Not all snacks are harmful. Research shows that healthy snacks can improve overall diet quality. Nuts, fruit, yogurt, hummus and vegetables provide fibre, protein and healthy fats that promote fullness without blood sugar spikes.

2. We need to eat more protein

Most Americans already consume enough protein. Recommended intake is roughly 0.75 to 1.0 grams per kilogram of body weight per day (about 45 to 70 grams for most women and 55 to 90 grams for most men).

Protein powders aren’t a solution either. In one analysis, two-thirds of tested protein powders contained unsafe levels of lead. There are exceptions:

Adults over 60, who lose muscle mass with age, may benefit from about 1.2 g/kg

Athletes or people recovering from illness may need up to 1.5 g/kg

For everyone else, whole-food sources (beans, lentils, yogurt, fish) are safer and more beneficial than supplements or excessive red meat.

3. Fibre supplements work just as well as whole foods

Only about 7 per cent of adults meet recommended fibre intake, and that’s a serious problem.

High-fibre diets are linked to lower risk of colorectal cancer, reduced rates of Type 2 diabetes, and a 31 per cent lower risk of death from coronary heart disease.

But fibre supplements aren’t a perfect shortcut. Most contain just one type of fibre and don’t replicate the complex, diverse fibres found in whole foods. Only a small fraction show meaningful clinical benefits.

Fruits, vegetables, beans and whole grains remain the most effective way to support gut health.

4. Low-fat dairy is always better

Dairy consumption is associated with lower risk of Type 2 diabetes and improved growth in children — regardless of fat content.

The idea that higher-fat dairy causes weight gain isn’t supported by evidence. In fact, studies show children who consume whole-fat dairy have lower odds of overweight and obesity than those consuming low-fat versions. Adults show similar trends.

Fat content alone doesn’t determine health. Whole-fat dairy can fit into a balanced diet, especially when it replaces ultra-processed “low-fat” alternatives.

Choose the version you enjoy and can sustain.

5. All fats are bad

For decades, people have been told fat makes you fat. This has been proven wrong. Yet as dietary fat intake declined, obesity and diabetes rates surged.

Healthy fats are essential. Many calorie-dense foods — nuts, olive oil, full-fat dairy, even dark chocolate — are associated with less weight gain than processed grains and sugary snacks.

Liquid plant oils, especially extra-virgin olive oil, have strong evidence behind them. Even half a tablespoon per day has been associated with a 19 per cent lower risk of death over nearly 30 years.

Fat isn’t the enemy. It’s the ultra-processed, low-fibre, high-sugar foods that drive weight gain and metabolic disease.

6. You can exercise off calories

Many people believe an extra workout can cancel out unhealthy eating. Unfortunately, you can’t. There’s more than a grain of truth to the saying, “you are what you eat.”

A recent study found that humans burn roughly the same number of calories per day regardless of activity level. Exercise improves health, but it doesn’t provide the calorie “bonus” people expect. What and how much you eat is what moves the needle on weight.

That said, exercise is still essential. It improves sleep, mood, cognition, bone density and social connection. Walking, especially with other people, is one of the most effective and accessible forms.

Good nutrition is simply about designing a life where healthy choices are ones that are easy and that you stick to for years: whole foods like fruits, nuts, and vegetables, modest portions and meals shared with people you like.

Skip the detoxes. Keep the olive oil. And yes, sometimes eat your ice cream.

Dr. Ezekiel J. Emanuel is an oncologist, Vice Provost and Professor of Medical Ethics and Health Policy at the University of Pennsylvania, and author of Eat Your Ice Cream: 6 Simple Rules for a Long and Healthy Life.