There’s no sugar-coating it: All calories are not created equal

Celia Smoak Spell
Celia Smoak Spell, Assistant Editor, Harvard Health Publications

Burning more calories each day than you consume may have been the diet advice from the past, but that doesn’t work for everyone.  Instead, the focus should be on eating whole foods and avoiding processed carbohydrates — like crackers, cookies, or white bread. A recent review in JAMA Internal Medicine further casts a light on the shaky history of nutritional science. Before the 1980s, regulations did not require researchers and physicians to declare conflicts of interest before publishing a paper. By not announcing affiliation, research had the potential to be swayed by money and funding. That’s why it had to change.

Are fat and cholesterol the dietary “bad guys”?

A study funded by the Sugar Research Foundation (SRF) from the 1960s found that cholesterol and fat were the main contributors to weight gain and responsible for an increased risk for coronary heart disease. These results kick-started the country’s decades-long consumption of added sugar. With fat removed, food lost taste and appeal, so manufacturers added sugar to combat this. The country’s intake of sugar and processed carbohydrates went up, while our intake of fat went down. Dr. David Ludwig, a professor in the Department of Nutrition at the Harvard T.H. Chan School of Public Health, says “Overall, these processed carbohydrates are worse than the fats they replaced.”

The JAMA review from September found that the doctors involved with the study were in fact paid by the SRF. Their research was tainted due to conflict of interest. The SRF — and thus the doctors paid by the SRF — directly benefited from the results of this 1960s study, and they profited tremendously from the uptick in sugar sales, while consumers made health decisions on the basis of questionable information.

The scoop on carbohydrates

It is true that fat has more calories than carbohydrates, including sugar. But by that logic, a sugary beverage is better for you than a handful of nuts. That’s just not what the unbiased studies have shown. Looking only at calories ignores the metabolic effects of each calorie; the source of the calorie changes how you digest it and how you retrieve energy from it.

Carbohydrates have been categorized as simple or complex in the past. Dr. Ludwig says these classifications are misleading. Many doctors are pulling away from those narrow categories and moving toward the all-encompassing terms of high glycemic index and low glycemic index. An apple is a simple carbohydrate because it is digested quickly by the body, but fruit is better for you than other simple carbohydrates like chips or crackers. That’s why Dr. Ludwig views the glycemic index as a more accurate measure of a food’s value (good or bad). When something has a low glycemic index, it raises your blood sugar levels slowly, increasing your insulin levels gradually.

That’s good, because too many insulin spikes result in insulin resistance, where your body stops responding to insulin it is producing (also known as type 2 diabetes). High-glycemic foods, on the other hand, cause blood sugar levels and thus insulin to rise quickly, prompting the overproduction of insulin and fat storage. Ludwig would rather you focus on low-glycemic foods like whole-grain pasta, wheat bread, fruits, beans, and nuts. High-glycemic foods include candy, croissants, and scones. By choosing the low-glycemic foods and thus the minimally processed foods, people can lose more weight, feel fuller longer, and remain healthier.

Can you make peace with fat?

Today you can look at food differently. Counting calories alone doesn’t work because ultimately it matters where those calories come from; this matters more than the number of calories ingested. Dr. Ludwig says, “It was this calorie-focus that got us into trouble with the low-fat diet in the first place.”

So don’t be afraid to go back to fat. Just make sure it’s the healthy fats like avocado, olive oil, and nuts. Don’t cut out the fat, and don’t make a habit of eating products labeled “fat free.”


  1. Dan Huck

    What gets me in trouble relates to a factor Dr. Ludwig talks about, but inadvertently, I assume, was not mentioned by the author of this article: glycemic load. Glycemic Load = Glycemic Index (%) x grams of carbohydrate per serving. Many commentators are “fighting back” because the glycemic index by itself, unrelated to serving size, leaves you wondering if serving sizes matter at all. But serving size, of course, is where calories come in to the equation. Staying away from high glycemic load (28) raisins, for me, is easier than being content with 1/4 cup (normal serving), while the longer sustenance obtained from a serving of strawberries, g.l. 1, or watermelon, g.l. 4, saves me from the sugar high and keeps me happier longer.

  2. David Harris

    Again, overly simplistic. Harvard Health lags behind public health research, nutrition being just one area. For example, a croissant has a GI ranging from 40-60, which makes it a low GI food choice, not a high GI food as you suggest. Get with it. For up to date information on GI facts, go to, a website of the Univesity of Sydney. As another example, you really missed a golden opportunity in your brief article about GI to talk of the health benefits associated with food blending (as in combinations of, not as in using a blender), which is a key to using the GI to guide healthy food choices.

  3. BelReigne proteinedieet

    Nice one but nowadays we’re bombarded with all kinds of health and weight loss ‘news’. It’s hard to filter out what is right and what is wrong….

  4. Adil

    in a normal measure of every day physical movement eats 3000 calories for every day they will get fat. On the off chance that they eat just 1500 calories for each day they won’t put on anyplace close as much weight. Calories do make a difference in weight control. Inside a slender utmost of +/ – 10% or so what the calories comprise of can have any kind of effect in helping your digestion system devour them.

  5. Richard

    Amazing that so many support olive oil when there is no evidence it is healthy but evidence that it reduces blood flow almost immediately after consumption. The known nutrients in olive oil are minuscule compared to whole plant-based products like olives, avocado, nuts and seeds…
    Considering the high number of calories for the 100% fat product why do so many insist on consuming it? Ohhh you like the taste! I bet milk chocolate taste good to many more than unprocessed cocoa too but that is again not a valid reason to consume so much of it…

  6. Richard

    There is good and bad information floating everywhere, including this article. Readers should not think calories do not matter relative to weight but what you eat is much more important for long term health than your weight.
    A very large percentage of the world population would be at their correct weight if they focused properly on whole plant-based products without counting calories but much more importantly there would be significantly less heart disease, diabetes and cancer to name just a few ailments.
    Salt does not contain many calories but a large number in the world are slowly killing themselves with the large amount of daily salt they consume. Trans fats may have more calories than salt but it also appears to be more deadly and likely should be banned and is in some countries.

    • Carroll Hoagland

      There is NO known carbohydrate deficiency disease, where as this is not true of proteins and fats, hence carbs are a Non-Essential macronutrient. That is why the LCHF ketogenic diet works and is curing everything from diabetes to cancer .. remember before insulin was invented i.e. a “Patentable Drug” we cured diabetes by avoiding carbs. We only have about 1 tsp of glucose dissolved in our blood … and insulin is really a growth hormone not designed to control the upper limit, is only controls the lower limit and triggers gluconeogenesis to support the nervous system.

      All this bogus science is the failure of the AMA, FDA, and NIH who have failed the patient …

      Simple … The AMA (the most powerful lobby in Washington) and NIH have failed the patient … Physicians have abandoned the nutritional approach to patient diagnostics and medicine, simply because they are not trained in nutrition. A key part of the Hippocratic Oath … “I will prevent disease whenever I can, for prevention is preferable to cure… “, has been forgotten …

      70 Going On 100 … the Centenarian Diet

  7. Gerda

    My mother was right… We drank cod liver oil in the bath tub in case we spilled it, ate one green and one yellow vegetable with dinner every night along with lean protein and a carb. We needed our roughage so fruit was not peeled and rice was brown. Soda was expensive so we drank water. She was a juvenile diabetic who lived into her 70s without most of the common diabetic complications.

  8. H.M. Saunders

    If the notion that burning more calories than you consume has been debunked as diet advice, then either the laws of physics have been repealed or there are still problems in nutritional science. If you consistently burn more calories than you consume, then the laws of physics say you must lose weight – calories cannot be created out of thin air, but only by the conversion of mass to energy. Are starving people delusional; they are not really emaciated when their intake is insufficient to generate the calories expended?
    If the research suggests that eating less than you burn will not lead to weight loss, then the measurement of one or both of these must be wrong. Nutrition tables are based on the assumption that protein and carbohydrate both yield 4 kilocalories per gram, 9 Kcal for fat and 7 Kcal per gram of alcohol. I am not clear on how the deduction for non-digestible fiber in carbohydrates is made but this deduction process could lead to inaccuracies in calculating actual caloric intake. There may also be differences in the percentage of available calories that the body takes up: for example, perhaps the body absorbs a higher percentage of the 4 Kcal per gram of easily digested high-glycemic index carbs and a lower percentage from low index foods which may transit the bowel before it is all absorbed. It seems highly likely that not all people absorb the same percentage of theoretically available calories in their foods – our guts are just too diverse.
    Even if researchers got the caloric UPTAKE right, the measurement of caloric expenditure is susceptible to estimation errors, since it is unlikely that all of the subjects in these studies spent their days hooked up to a calorimeter measuring oxygen consumption or carbon dioxide exhaled. Instead, average rates of caloric expenditure are applied per minute or hour of each type of activity. Even if you wear an accelerometer, there is a margin of error in estimating expended calories that may be significant.
    And of course, people lie about how active they are and how much they eat, so unless there are actual measurements, then the validity of the conclusion may be seriously compromised.
    While the article focuses on the shaky history of nutritional science, to me, the evidence so far is that things have improved but are still far from perfect. The one thing we should have learned is not that we don’t yet have all the answers, but that the answers we do have may not be correct – unless the laws of physics have been repealed..

    • Mark Jackman, PhD

      The low-fat craze certainly created a public health problem for the reasons you mention in your article. However, I feel this article oversimplifies things and will lead some people to be more confused. Calories do still matter insofar as they measure food energy. Eat too much food energy (calories), whether from protein, carbohydrates or fat, and you’ll gain weight at the margin. Yes, fatty foods like nuts are nutritious and healthier choices than chips. But, fatty foods are calorie dense and I have watched people gain significant weight by eating more than a small amount of nuts each day. So, food choices matter for lots of reasons including satiety and metabolic effects. But, calories still count (however you measure them, e.g. serving sizes and number). For example, when I dine out I often marvel at small women sitting next to large men and they are both eating the same too-large serving of food. Who do you guess is likely to gain more excess body fat with that behavior? Refined carbohydrates may have something to do with it, but it’s hard to ignore the relative surplus of food energy she’s consuming for her height and weight.

    • Didi Groen D.D.S.

      I am sorry but from personal experience I can tell you my moderate to high fat diet which comes to between 3,000-5,000 calories is how I maintain 115 pounds (5’8″). I learn about this from Peter Atiia, MD. I am 57, and a T1D for 28 years ( gestational). I was doing poorly on the diet Joslin had me on and took matters into my own hands. 6 months later my blood work looks so much better and my renal specialist said whatever you are doing stay with it-you are on your way. I should add I am a life time athlete and scull, Pilates, tennis, box,,etc -do something every day. I just can’t get enough movement. Carbs are below 50 and try to stay around 25 but am flexible. Each body is unique. This is what works for me. With your MD’s permission/guidance I suggest people try it. Easy enough to stop if isn’t producing desirable results. I am a retired dentist with a strong medical background.

    • Fernando Saravi

      I fully agree with Mr. Saunders. Of course, the source of energy, the way food is digested and nutrients are absorbed, as well as their effect on insulin secretion, etc., should be taken into account. But having said that, it should be painfully obvious that if you spend 2500 kcal per day and get 1500 per day from food long enough , you will inexorably lose weight. It’s thermodynamics, it’s physics. Biological systems – including our own bodies – are very complex but they cannot go against thermodynamics.

    • Robert Bramel

      Think of this: Everyone understands that virtually all features of human biology are controlled by genetic expression of things like hormones– height, liver size, hair follicles, outer ear dimensions, and so on: everything, except that some people believe that fat deposition and amount is inexplicably nothing more than an unregulated response to food intake. Never mind all the counter examples to this idea: a calorie in is either burned or it is turned into fat. How ridiculous! A thoughtful consideration of all the other possibilities shows that a hormonally controlled body has many more options than simply turning a calorie of food into fat. How about the gut absorbing less efficiently if calories are not needed. We know, for example, that kidneys respond to different levels of water availability by changing urine concentration. So far as I have read, nobody’s bothered to measure caloric extraction efficiency as a function of body needs. Probably the gut just reduces efficiency when calories aren’t needed. How about increasing heat loss by increasing slightly blood flow to the skin surface. Increased heat loss certainly disposes of excess calories. These two options alone demolish the notion that ingested calories have to go to fat cells.

      So what actually controls the amount of fat if it isn’t just the amount we eat? Scientists have known for decades that serum insulin plays a major role instructing fat cells to remove fuel from the blood stream and create triglycerides within the fat cell. Oh wow! Insulin is a hormone. So, in fact, fat tissue is hormonally controlled, just like all the other features of the body. Surprise, surprise!

  9. Hilton Aumüller

    Will there one day be a definitive conclusion? I
    ‘m afraid I’ll die before knowing the truth…. I think about eggs, coffee…

    • Richard

      We will all be gone in the 100 to 500 years it will take at present pace to know exactly what the almost perfect diet is. The length of time needed is the fault of our government and the food industry that both have other agendas other than our health.
      Why has the US government supported meat and sugar production but not kale or spinach??? Why does our government continue talking about lowering health costs but continue supporting money going to a medical field that prefers expensive and often ineffective methods compared to good nutrition?
      We all should know why the food industry loves meat, sugar, salt and harmful additives…

  10. Mike Clipp

    Quantity for weight control, quality for health. I think that those who proclaim that calories don’t matter are doing a disservice to their readers. If a 5’2″ person who engages in an average amount of daily physical activity eats 3000 calories per day they will get fat. If they eat only 1500 calories per day they won’t gain anywhere near as much weight. Calories do matter in weight control. Within a narrow limit of +/- 10% or so what the calories consist of can make a difference in helping your metabolism consume them. When you ingest 50% to 100% more calories than you should their type doesn’t make much difference. You will gain a lot of weight. Yes, if you eat a good plant based diet you probably will be healthier than the person who eats 3000 calories of junk food but you will still gain weight.

  11. Elaine

    To this 76 yr old healthy female, any diet advice that culminates in promotion of avocados, almonds/nuts, and olive oil is flawed. Avocados and almonds are headlines in climate change and water shortages. Olive oil is elitist, in practical terms. So I have to ignore this just like I did much of the fat scare and much other nutrition expert advice.

    • Mary

      I understand and applaud your concern for the water expenditure involved in almonds (but not all nuts) and avocados, but I cook with nothing but olive oil, which is easy on the environment, and make salad dressing with nothing else. It’s not elitist. I use it because I have naturally high cholesterol and can’t take statins for medical reasons. I spend maybe $15 a year on olive oil–and I don’t skimp! Most people can afford $15 a year. It’s good for you, it’s yummy, it requires little water to produce and supports small-scale growers. What’s not to like?

    • vicki Lindner

      If olive oil is elitist why do so many in Italy, Spain and Portugal use it?

  12. Stephen Feher

    Just as all calories are not created equal, so all fats are not created equal. There have been many recommendations for increasing Omega 3 fats to diet, but this recommendation is an effort to make up for the overconsumption of Omega 6 fats that are pro-inflammatory. Omega 3 fats are anti-inflammatory. It is the ratio of Omega 6 to Omega 3 fats that is important, and while some of the fats mentioned in the paper are considered healthy, portion sizes and the ratio of Omega 6 to Omega 3 must be considered.