Your bodyweight depends on your total caloric intake more than on your macronutrient ratios (how many of your calories come from carbohydrates, proteins, fats, and alcohol). Increased caloric intake as an independent variable is more than sufficient to explain the current obesity epidemic, without the need to find a scapegoat, such as high-fructose corn syrup.
A trial in a controlled setting (a metabolic ward) compared several isocaloric diets composed of 15% protein, 15-85% carbohydrate, and 0-70% fat. It concluded that caloric restriction, not macronutrient ratios, determined weight loss. Comparing low- and high-carbohydrate diets over 6 weeks and 12 weeks led to the same conclusion, as did comparing a low-fat/high-protein diet with a high-fat/standard-protein diet.
Another trial in a metabolic ward noted that, in healthy individuals overeating for 8 weeks, caloric intake alone accounted for the increase in body fat. However, caloric expenditure, total weight, and lean mass increased with protein as a percentage of caloric intake. In contrast, a previous study on the impact of protein on weight loss had noted that women lost as much weight on a high-protein diet as on a high-carb diet, but that subjects with high triglycerides lost more fat on the high-protein diet.
In people suffering from hyperinsulinemia, insulin resistance, or type-2 diabetes, the results are mostly the same: Caloric restriction, not macronutrient ratios, leads to weight loss. Two studies noted, however, that lean mass was better preserved in women (but not men) on a high-protein diet, and one study did find a greater weight loss (nearly entirely from fat) in the high-protein group (men and women).
Independent of your diet’s macronutrient ratios, a negative energy balance (consuming fewer calories than your body needs) is responsible for weight loss.
Many diets, fad or not, do work. This is mainly because they reduce calories.
Several diets restrict your carbohydrate intake. The ketogenic diet is very high in fats, low in proteins, and very low in carbohydrates. The Atkins diet is high in fats, high in proteins, and very low in carbohydrates. The “paleo diet” (hunter-gatherer diet) is high in fats, high in proteins, and low in carbohydrates.
Fats and proteins digest more slowly than carbohydrates, so are more satiating. In addition, most diets (including the three already mentioned) recommend the consumption of foods that are less calorie-dense (more fibers and a higher water content: a pound of broccoli packs less calories than a pound of grains). Finally, carbohydrates participate in the synthesis of serotonin, which can cause cravings in some obese individuals.
You can also refer to our page on how much protein you need per day to figure out the exact number.
Therefore, people on a low-carb diets lose weight because they naturally eat less and avoid the large binges caused by carbohydrate cravings. People on very-low-carb diets can also lose weight very quickly on the short term because the depletion of their glycogen stores leads to the excretion of bound water. That explains why two trials found that people on a low-carb diet had lost more weight than people on a low-fat diet after 6 months but not 12.
Consuming your macronutrients together (balanced diet) or separately (dissociated diet, also known as “food combining”) makes no difference with regard to weight or fat loss.
Since prolonged fasting might increase heat expenditure, diets that manipulate fasting (Intermittent Fasting, Alternate Day Fasting) may have some benefits on the “calories out” side of things. Yet, even here, weight lost is mostly due to the fact that you control eating: It is much harder to overeat in 8 hours than in 16.
A worthwhile read is a major study that showed a low-fat versus a low-carb diet did not matter for weight loss.
For more information on what you need to eat for weight loss, see our Fat Loss Stacks page.
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- Increased food energy supply is more than sufficient to explain the US epidemic of obesity. Am J Clin Nutr. (2009) Swinburn B, Sacks G, Ravussin E.
- Lack of evidence for high fructose corn syrup as the cause of the obesity epidemic.
- Energy intake required to maintain body weight is not affected by wide variation in diet composition. Am J Clin Nutr. (1992) Leibel RL, et al.
- Similar weight loss with low- or high-carbohydrate diets. Am J Clin Nutr. (1996) Golay A, et al.
- Weight-loss with low or high carbohydrate diet. Int J Obes Relat Metab Disord. (1996) Golay A, et al.
- Carbohydrate-restricted diets high in either monounsaturated fat or protein are equally effective at promoting fat loss and improving blood lipids. Am J Clin Nutr. (2005) Luscombe-Marsh ND, et al.
- Effect of dietary protein content on weight gain, energy expenditure, and body composition during overeating: a randomized controlled trial. JAMA. (2012) Bray GA, et al.
- Effect of an energy-restricted, high-protein, low-fat diet relative to a conventional high-carbohydrate, low-fat diet on weight loss, body composition, nutritional status, and markers of cardiovascular health in obese women. Am J Clin Nutr. (2005) Noakes M, et al.
- Long-term weight maintenance and cardiovascular risk factors are not different following weight loss on carbohydrate-restricted diets high in either monounsaturated fat or protein in obese hyperinsulinaemic men and women. Br J Nutr. (2007) Keogh JB, et al.
- Effect of a high-protein, energy-restricted diet on body composition, glycemic control, and lipid concentrations in overweight and obese hyperinsulinemic men and women. Am J Clin Nutr. (2003) Farnsworth E, et al.
- Long-term effects of a high-protein, low-carbohydrate diet on weight control and cardiovascular risk markers in obese hyperinsulinemic subjects. Int J Obes Relat Metab Disord. (2004) Brinkworth GD, et al.
- Effects of moderate variations in macronutrient composition on weight loss and reduction in cardiovascular disease risk in obese, insulin-resistant adults. Am J Clin Nutr. (2006) McLaughlin T, et al.
- Effect of high protein vs high carbohydrate intake on insulin sensitivity, body weight, hemoglobin A1c, and blood pressure in patients with type 2 diabetes mellitus. J Am Diet Assoc. (2005) Sargrad KR, et al.
- Effect of a low-carbohydrate diet on appetite, blood glucose levels, and insulin resistance in obese patients with type 2 diabetes. Ann Intern Med. (2005) Boden G, et al.
- Effect of energy restriction, weight loss, and diet composition on plasma lipids and glucose in patients with type 2 diabetes. Diabetes Care. (1999) Heilbronn LK, Noakes M, Clifton PM.
- Effect of a high-protein, high-monounsaturated fat weight loss diet on glycemic control and lipid levels in type 2 diabetes. Diabetes Care. (2002) Parker B, et al.
- Scientific evidence of diets for weight loss: Different macronutrient composition, intermittent fasting, and popular diets. Nutrition. (2020) Freire R.
- The effect of a hypocaloric diet with and without exercise training on body composition, cardiometabolic risk profile, and reproductive function in overweight and obese women with polycystic ovary syndrome. J Clin Endocrinol Metab. (2008) Thomson RL, et al.
- Fat loss depends on energy deficit only, independently of the method for weight loss. Ann Nutr Metab. (2007) Strasser B, Spreitzer A, Haber P.
- Atkins and other low-carbohydrate diets: hoax or an effective tool for weight loss. Lancet. (2004) Astrup A, Meinert Larsen T, Harper A.
- Similar weight loss with low-energy food combining or balanced diets. Int J Obes Relat Metab Disord. (2000) Golay A, et al.