First we were taught to fear fat. It kind of made sense, given the name. Fat must be fattening, right?
Recently, the tide has turned. Carbs are now the fattening, evil macronutrient du jour. Carbs are the new fat.
But condemning either fat or carbs is preposterous.
Discounting alcohol (who can?), there are only three major calorie sources: fat, protein, and carbs.
Protein is not primarily used for energy.631
That leaves only two major energy sources: fat and carbs.
Is it wise to indict one of two major energy sources?
A 2014 meta-analysis of 48 randomized diet trials concluded:
Significant weight loss was observed with any low-carbohydrate or low-fat diet. Weight loss
differences between individual named diets were small. This supports the practice of recommending any diet that a patient will adhere to in order to lose weight.632
Both low-fat and low-carb diets can work.
Since there are only two major energy sources, any diet that severely restricts either one is likely to be effective. (Though low-carb diets may be more effective than low-fat diets.633,634 )
But while some people can make low-carb or low-fat dieting a lifestyle, for most of us, they’re just a short-term thing.
And just because low-fat and low-carb diets work, that doesn’t make fat or carbs inherently fattening.
In one illuminating study, patients were kept in hospital wards and fed liquid meals of varying amounts of fat, carbs, and protein. Each day, their calorie intake and body weight were measured precisely.
Protein was kept at a flat 15% of total calories, while fat and carbs were varied over huge ranges. Fat was dialed from 0% to 70% of total calories, and carbohydrate was dialed from 15% to 85% of total calories, with various percentages in between.635
These diets lasted an average of 32 days.
The main finding? Regardless of the amount of fat or carbs in the patients’ diets, no differences in body weight were found between the diets.
The only number that mattered? Total calories.
In Defense of Fat
The Maasai are a cattle-herding African tribe who subsist almost entirely on meat and milk. They eat lots of fat, and lots of saturated fat. Their diet is 66% fat.636
This is extraordinarily high. It’s roughly double the average American’s fat intake.637
Are the Maasai fat?
If anything, the Maasai are underweight.638
Similarly, the Arctic-dwelling Inuit were forced to subsist mostly on aquatic animal food before contact with the industrialized world. Their diet was necessarily high in fat.
Were the Inuit fat? Only four percent of Inuit men were overweight as late as the 1960s.639
Along the same lines, modern hunter-gatherers generally eat as much or more fat than Westerners.640
They rarely have any sort of weight problems.
This ethnographic evidence indicates that whole-food fat is not inherently fattening. While it doesn’t mean that slathering your food with butter will help you lose weight, it does indicate that even large amounts of fat in the context of protein-rich whole foods can be compatible with leanness.
In 1998, superstar Harvard nutrition researcher Walter Willett published a review of many nutrition studies in the American Journal of Clinical Nutrition. He concluded:
Diets high in fat are not the primary cause of the high prevalence of excess body fat in our society, nor are reductions in dietary fat a solution.641
Two decades later, Willett’s opinion hasn’t changed.642
Despite popular belief in the low-carb community, low-fat dieting was based on real, legitimate science.
Many controlled trials have found that if people eat as much as they want, they’ll eat more—and weigh more—on diets high in fat than diets high in carbs.643,644,645,646,647,648,649
(At least in the short term.)
So the low-fat thing wasn’t pulled out of thin air.
But there are major caveats. The studies supporting the idea that high-fat diets are fattening generally used processed foods.650,651,652,653,654 In many of these studies, the fat used to make the diets “high-fat” was vegetable oil.655,656,657
Several of these trials featured scones, muffins, and puddings.
Diets with “high-fat” foods like those tell us little about the fat in meat, dairy products, and nuts—the kind ensconced in protein (the most filling macronutrient).
But in typical reductionist fashion, these trials were used as evidence to indict all fat. Food companies responded, sucking the fat out of foods (even whole foods), adding lots of sugar, and branding them “low-fat.”
To say the least, this didn’t stop the obesity epidemic.
In fact, studies have shown that eating foods labeled “low fat” actually causes people to eat more total calories.658 People may think low-fat foods are healthier, so they have a license to eat more. But “low fat” usually just means “high sugar.”
Which means “fattening.”
Still, the evidence supporting low-fat diets does show that added fat is quite fattening. Many people fixate on refined carbs, oblivious to the dangers of added fat. As we’ve seen, between 1980 and 2010, soaring obesity rates increased in lockstep with increasing intake of added fat.
Due to its higher calorie density, added fat may be even more fattening than added sugar. (Check ingredients lists for any “oil.”) Many processed foods combine added fat and refined carbs—the perfect storm for weight gain and obesity.
In Defense of Carbs
Fruit is almost entirely carbohydrate—mostly sugar. Due to its high sugar content, many nutrition authorities have told us to avoid eating too much fruit. This is full-blown reductionist thinking—“all fructose bad.” The idea that fruit is contributing to obesity is incompatible with the theory of evolution, as well as a good deal of scientific evidence.
In fact, it’s downright absurd.
Of all the foods we eat today, the most ancient is probably fruit. We’ve been eating fruit for around 60 million years.659
Talk about being adapted to a food.
Fruit has fiber and vitamins, and there isn’t a shred of evidence that eating fruit causes weight gain, obesity, or diabetes.
In fact, it’s just the opposite. Eating more fruit reduces the likelihood of obesity660 and diabetes,661 and fruit is very filling.662
Despite being perceived as slightly less healthy than vegetables, eating fruit is associated with just as much of a reduction in heart-disease risk and all-cause mortality as eating vegetables.663
In the context of fruit, at least, sugar is not fattening.
(Note: juice is not fruit.)
So eat as much fruit as your heart desires, any time it desires it. This goes for any fruit: watermelon, pineapple, whatever.
There isn’t a shred of convincing evidence to do anything else.
Whatever differences may exist between fruits are trivial compared to the difference between any fruit and processed foods.
Aside from fruit, humans may have been eating starch-rich tubers as a staple food for over a million years. Some eminent anthropologists believe tubers were so important to our evolutionary success that it was actually cooking tubers—not meat—that was the main impetus for controlling fire.664
(Potatoes are tubers.)
Tubers are very high in carbs. But despite eating lots of tubers since forever, widespread human obesity is a very recent problem.
But enough theory. We have direct evidence of entire human societies eating sky-high-carb diets year-round, and being almost universally skinny and healthy.
The skinny Kitavans we met last chapter ate a diet of around 69% carbs665—again, mainly from tubers and fruit.
Were the Kitavans skinny-fat? Did their feathery weights belie some sort of carb-induced health problems?
The evidence suggests a hard no.
In Kitava, heart disease and stroke were virtually nonexistent.666 This is despite over 75% of Kitavans being daily smokers.667
You really can’t explain the Kitavans away. They ate tons of carbs every day, weren’t terribly active, and were thin as rails.
And before you can say “genes,” there were two cases of abdominal obesity seen in Kitava. Only two. Both bulging bellies belonged to Kitavan men who were only visiting Kitava during the study, and were actually living abroad—and eating a processed, “modern” diet.668
This suggests that it’s the traditional Kitavan diet—not great genes—that’s the secret sauce.
We met the Hadza awhile back. They’re hunter-gatherers in Tanzania. Similar to the Kitavans, about 68% of the Hadza diet is carbs. Remarkably, about 50% of their diet is sugar (mainly from honey and fruit).669
Talk about an atomic fructose bomb—every day, for life.
But similar to the Kitavans, the average Hadza BMI is just over 20.670
And as we saw, the Hadza aren’t lean because they’re “burning off” all those carbs.
The Murapin of Papa New Guinea were a community of farmers and pig-herders who were studied in the 1960s and ’70s. This is not a misprint: the average Murapin’s diet was 94.6% carbs, mostly from sweet potatoes.671
This amount of carbs is almost sickening. The average Murapin man ate 543 grams of carbs a day—a year-round carbicide. If carbs were the least bit fattening, the Murapin would have been morbidly obese.
Were they? At ages 20-29, Murapin men weighed an average of 132 pounds, while Murapin women weighed 112 pounds. And unlike us, their weights declined with age.672
Heart disease was rare among the Murapin, and diabetes was nonexistent.673 Murapin men ate an average of 2300 calories a day,674 which is fairly reasonable for a 132-pound man.675
It’s not like they were starving or something.
And there you have it. Three living, breathing human populations who ate cartoon amounts of carbs, were thin as rails, and healthy as horses.
Despite what many people say about carbs, most epidemiological studies show that the higher the proportion of carbs in someone’s diet, the less they weigh.676,677
This doesn’t prove that eating more carbs will make you thin.
But it does indicate that carbs don’t inherently make people fat.
Ketogenic (“keto”) diets are currently quite popular. Keto diets are high in fat and very low in carbs, and they seem to work for many people.678 The name derives from ketosis, a state that can happen on very-low-carbohydrate diets where the body switches to burning mostly fat for energy.679
Burning fat may sound like a sure-fire way to lose fat, but it really isn’t. Just because you’re burning fat for energy doesn’t mean you’re losing fat; the fat could just as easily be coming from your diet rather than the fat on your body. People confuse these two.
Unless you’re in a calorie deficit, you won’t lose any fat—even if you’re in ketosis. Indeed, a strictly controlled 2006 trial found that ketosis had “no metabolic advantage” over a non-ketogenic, low-carb diet.680 A 2016 trial found that, compared with a high-carb diet with equal calories, a ketogenic diet was “not accompanied by increased body fat loss.”681
Studies have found that ketogenic diets lead to less hunger,682 which can certainly lead to fat loss over time. Most importantly, perhaps, nearly every junk food has carbs. When you eliminate all carbohydrates, you eliminate all processed junk food. And it’s this elimination of processed junk food, not the alleged metabolic magic of ketosis, that’s the main reason for keto’s success.
The Maasai weren’t eating fat, they were eating meat and drinking milk. The Murapin weren’t eating carbs, they were eating sweet potatoes.The Hadza weren’t eating sugar, they were eating fruit and honey.
The Kitavans weren’t eating starch, they were eating tubers.
Natural whole foods like these—the kind we’ve been eating for millions of years—aren’t fattening.
Carbs aren’t fattening.
Fat isn’t fattening.
Don’t worry about fat or carbs.
Instead, worry about processed fat (vegetable oil) and processed carbs (white flour and added sugar) in processed food (food with more than one ingredient).
Those are the only fat and carbs to worry about.
631. Frayn, Keith. Metabolic Regulation: A Human Perspective. Oxford: Wiley Blackwell, 2010 Kindle File, 7.3, Location 4399 of 9142.
632. Johnston et al., “Comparison of Weight Loss Among Named Diet Programs in Overweight and Obese Adults: A Meta-Analysis,” JAMA 312, no. 9 (2014): 923-933.
633. Sackner-Bernstein et al., “Dietary Intervention for Overweight and Obese Adults: Comparison of Low-Carbohydrate and Low-Fat Diets. A Meta-Analysis,” PLOS One 10, no. 10 (2015): e0139817.
634. Mansoor et al., “Effects of Low-Carbohydrate v. Low-Fat Diets on Body Weight and Cardiovascular Risk Factors: A Meta-Analysis of Randomised Controlled Trials,” British Journal of Nutrition 115, no. 3 (2016): 466-479.
635. Leibel et al., “Energy Intake Required to Maintain Body Weight is Not Affected by Wide Variation in Diet Composition,” American Journal of Clinical Nutrition 55, no. 2 (1992): 350-5.
636. Biss et al., “Some Unique Biologic Characteristics of the Masai of East Africa,” New England Journal of Medicine 284, no. 13 (1971): 694-9.
637. “Diet/Nutrition,” National Center for Health Statistics. CDC. https://www.cdc.gov/nchs/fastats/diet.htm
638. Ngoye et al., “Differences in Hypertension Risk Factors between Rural Maasai in Ngorongoro and Urban Maasai in Arusha Municipal: A Descriptive Study,” Journal of Applied Life Sciences International 1, no. 1 (2014): 17-31.
639. Mouratoff G.J., and Scott E.M., “Diabetes Mellitus in Eskimos After a Decade,” JAMA 226, no. 11 (1973): 1345-6.
640. Cordain et al., “Plant-Animal Subsistence Ratios and Macronutrient Energy Estimations in Worldwide Hunter-Gatherer Diets,” American Journal of Clinical Nutrition 71, no. 3 (2000): 682-692.
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643. Stubbs et al., “Covert Manipulation of Dietary Fat and Energy Density: Effect on Substrate Flux and Food Intake in Men Eating Ad Libitum,” The American Journal of Clinical Nutrition 62, no. 2 (1995): 316-329.
644. Tremblay et al., “Impact of Dietary Fat Content and Fat Oxidation on Energy Intake in Humans,” American Journal of Clinical Nutrition 49, no. 5 (1989): 799-805.
645. Lissner et al., “Dietary Fat and the Regulation of Energy Intake in Human Subjects,” American Journal of Clinical Nutrition 46, no. 6 (1987): 886-92.
646. Proserpi et al., “Ad Libitum Intake of a High-Carbohydrate or High-Fat Diet in Young Men: Effects on Nutrient Balances,” American Journal of Clinical Nutrition 66, no. 3 (1997): 539-545.
647. Blundell et al., “Dietary Fat and the Control of Energy Intake: Evaluating the Effects of Fat on Meal Size and Postmeal Satiety,” American Journal of Clinical Nutrition 57, no. 5 (1993): 772S-777S.
648. Gerhard et al., “Effects of a Low-Fat Diet Compared with Those of a High-Monounsaturated Fat Diet on Body Weight, Plasma Lipids and Lipoproteins, and Glycemic Control in Type 2 Diabetes,” American Journal of Clinical Nutrition 80, no. 3 (2004): 668-673.
649. Kendall et al., “Weight Loss on a Low-Fat Diet: Consequence of the Imprecision of the Control of Food Intake in Humans,” American Journal of Clinical Nutrition 53, no. 5 (1991): 1124-1129.
650. Proserpi et al., “Ad Libitum Intake of a High-Carbohydrate or High-Fat Diet in Young Men: Effects on Nutrient Balances,” American Journal of Clinical Nutrition 66, no. 3 (1997): 539-545.
651. Blundell et al., “Dietary Fat and the Control of Energy Intake: Evaluating the Effects of Fat on Meal Size and Postmeal Satiety,” American Journal of Clinical Nutrition 57, no. 5 (1993): 772S-777S.
652. Lissner et al., “Dietary Fat and the Regulation of Energy Intake in Human Subjects,” American Journal of Clinical Nutrition 46, no. 6 (1987): 886-92.
653. Gerhard et al., “Effects of a Low-Fat Diet Compared with Those of a High-Monounsaturated Fat Diet on Body Weight, Plasma Lipids and Lipoproteins, and Glycemic Control in Type 2 Diabetes,” American Journal of Clinical Nutrition 80, no. 3 (2004): 668-673.
654. Kendall et al., “Weight Loss on a Low-Fat Diet: Consequence of the Imprecision of the Control of Food Intake in Humans,” American Journal of Clinical Nutrition 53, no. 5 (1991): 1124-1129.
655. Blundell et al., “Dietary Fat and the Control of Energy Intake: Evaluating the Effects of Fat on Meal Size and Postmeal Satiety,” American Journal of Clinical Nutrition 57, no. 5 (1993): 772S-777S.
656. Lissner et al., “Dietary Fat and the Regulation of Energy Intake in Human Subjects,” American Journal of Clinical Nutrition 46, no. 6 (1987): 886-92.
657. Gerhard et al., “Effects of a Low-Fat Diet Compared with Those of a High-Monounsaturated Fat Diet on Body Weight, Plasma Lipids and Lipoproteins, and Glycemic Control in Type 2 Diabetes,” American Journal of Clinical Nutrition 80, no. 3 (2004): 668-673.
658. Wansink, B., “Can ‘Low-Fat’ Nutrition Labels Lead to Obesity?” Journal of Marketing Research 43, no. 4 (2006): 605- 617.
659. Klein, Richard. The Human Career: Human Biological and Cultural Origins. Chicago: University of Chicago Press, 1999.
660. He et al., “Changes in Intake of Fruits and Vegetables in Relation to Risk of Obesity and Weight Gain Among Middle-Aged Women,” International Journal of Obesity 28 (2004): 1569-1574.
661. Bazzano et al., “Intake of Fruit, Vegetables, and Fruit Juices and Risk of Diabetes in Women,” Diabetes Care 31, no. 7 (2008): 1311-1317.
662. Holt et al., “A Satiety Index of Common Foods,” European Journal of Clinical Nutrition 49, no. 9 (1996): 675-690.
663. Aune et al., “Fruit and Vegetable Intake and the Risk of Cardiovascular Disease, Total Cancer, and All-Cause Mortality—A Systematic Review and Dose-Response Meta-Analysis of Prospective Studies,” International Journal of Epidemiology (2016): doi: https://doi.org/10.1093/ije/dyw319
664. Derr, Mark, “Of Tubers, Fire and Human Evolution,” New York Times. 01-16-2001. https://www.nytimes.com/2001/01/16/science/of-tubers-fire-and-human-evolution.html
665. Lindeberg et al., “Age Relations of Cardiovascular Risk Factors in a Traditional Melanesian Society: The Kitava Study,” American Journal of Clinical Nutrition 66, no. 4 (1997): 845-852.
667. Lindeberg et al., “Cardiovascular Risk Factors in a Melanesian Population Apparently Free from Stroke and Ischaemic Heart Disease: The Kitava Study,” Journal of Internal Medicine 236, no. 3 (1994): 331-340.
668. Lindeberg, Staffan. Food and Western Disease: Health and Nutrition from an Evolutionary Perspective. Hoboken: Wiley-Blackwell, 2010. Kindle File, Chapter 4.5, Location 3103 of 11554.
669. Marlowe et al. “Honey, Hadza, Hunter-Gatherers, and Human Evolution,” Journal of Human Evolution 71 (2014): 119- 128.
670. Marlowe, F.W., and Berbesque, J.C., “Tubers as Fallback Foods and their Impact on Hadza Hunter-Gatherers,” American Journal of Physical Anthropology 4 (2009): 751-8.
671. Trowell, H.C., and Burkitt, D.P. Western Diseases: Their Emergence and Prevention. Cambridge: Harvard University Press, 1981. Page 174.
672. Ibid., page 175.
673. Ibid., pages 180-181.
674. Ibid., page 174.
675. “Learn How Many Calories You Burn Every Day,” TDEE CALCULATOR. https://tdeecalculator.net/
676. Gaesser, G., “Carbohydrate Quantity and Quality in Relation to Body Mass Index,” Journal of the American Dietetic Association 107, no. 10 (2007): 1768-80.
677. Merchant et al., “Carbohydrate Intake and Overweight and Obesity Among Healthy Adults,” Journal of the American Dietetic Association 109, no. 7 (2009): doi: 10.1016/j.jada.2009.04.002.
678. Bueno et al., “Very-Low-Carbohydrate Ketogenic Diet v. Low-Fat Diet for Long-Term Weight Loss: A Meta-Analysis of Randomised Controlled Trials,” British Journal of Nutrition 110, no. 7 (2013): 1178-1187.
679. Westman et al., “A Review of Low-Carbohydrate Ketogenic Diets,” Current Atherosclerosis Reports 5, no. 6 (2003): 476-483.
680. Johnston et al., “Ketogenic Low-Carbohydrate Diets Have No Metabolic Advantage over Non-Ketogenic Low-Carbohydrate Diets,” American Journal of Clinical Nutrition 83, no. 5 (2006): 1055-1061.
681. Hall et al., “Energy Expenditure and Body Composition Changes after an Isocaloric Ketogenic Diet in Overweight and Obese Men,” American Journal of Clinical Nutrition 104, no. 2 (2016): 324-333.
682. Sumithran et al., “Ketosis and Appetite-Mediating Nutrients and Hormones After Weight Loss,” European Journal of Clinical Nutrition 67 (2013): 759-764.