The best fat loss diet is based on the best available scientific principles and evidence.
Unlike most other popular diets, the best weight loss diet outlined here is 1) supported by basic science and randomized trials, 2) proven effective in real-world application, and 3) capable of meeting basic micronutrient requirements.
The best fat loss diet must meet two requirements:
Negative energy balance means that your energy intake is less than your energy expenditure.
This is an absolute requirement for weight loss on the best fat loss diet. You simply can not reduce body weight without a negative energy balance, also known as caloric deficit.
Your body fat is stored energy, and operate exactly like a savings bank. Your body fat is an energy bank.
We measure dietary energy as kilocalories (kcal) or joules. Usually we just use "calories" for kcal when dealing with dietary energy.
A pound of fat (dietary or body fat) supplies about 3500 kcal. Thus, if you consume 3500 calories more than you need, you will gain a pound of fat; and if you create a 3500 calorie energy deficit or negative energy balance, you will lose a pound of body fat.
In reality there is no way around energy balance. It is simple physics and math.
Just as positive cash balance means you have a cash income greater than cash expenditure, a positive fat balance means you have a fat intake greater than fat expenditure.
Just as negative cash balance means you have a cash expenditure greater than cash income, negative fat balance means you have a fat expenditure greater than fat intake.
Obviously, to reduce body fat you must have a negative fat balance.
How do you expend fat? Contrary to popular belief, you don't have to do anything special with your diet or physical activity to expend fat. Regardless of your diet, you expend fat just staying alive and carrying out all the activities of your life.
A standard college-level nutrition textbook states that in people eating “normal” mixed diets containing more than 150 g of carbohydrate daily, fats provide about 60% of ongoing energy needs; the balance of 40% is provided primarily by glucose. Moreover, this increases to at least 70% when people engage in low- to moderate-intensity aerobic activity.1
A 2014 study reported that lean and obese individuals eating high carbohydrate diets obtain about 45% of energy from fat and 43% from carbohydrate on a sedentary day, which changes to 49% fat and 39% carbohydrate on days that included 30-60 minutes of moderate-intensity exercise. 2
The human body naturally burns fat. However, if you eat more fat than you burn, your fat bank will grow. If you want to reduce your fat bank you have to eat less fat than you burn. A negative fat balance is an absolute requirement for the best fat loss diet.
Protein, carbohydrate and fat all provide energy. You can create a negative energy balance by restricting dietary protein, carbohydrate or fat. What is preferable for the best fat loss diet?
For the best fat loss diet restricting protein is not advisable because you need protein to maintain your lean mass, and multiple studies suggest that dietary protein contributes only to lean mass, not fat mass.3, 4, 5
That leaves the choice between limiting carbohydrate or fat. Which path leads to the best fat loss diet?
Restricting carbohydrate intake below carbohydrate expenditure produces a negative carbohydrate balance – you expend more carbohydrate than you ingest – not a negative energy balance. This directly depletes your glycogen stores, not your fat stores!
By depleting glycogen, restricting carbohydrate will negatively impact your ability to perform resistance exercise.11 Moreover, dietary carbohydrate itself is only rarely converted to body fat because the body will either use it for energy, expend it to generate heat, or store it as glycogen. 6, 7
At this point it should be obvious that restricting fat intake is the most direct way to create a negative fat balance and the best fat loss diet. Research shows that dietary fat intake, not carbohydrate intake, regulates energy intake and adiposity.3 Calorie for calorie fat is less satisfying (easier to overeat) than either protein or carbohydrate,13 and excess dietary fat contributes to excess body fat more effectively than either protein or carbohydrate.14, 15
Its simple. Fat has 9 kcal per gram, whereas carbohydrate has only 4 kcal per gram. Therefore, fat in your diet most directly determines the energy (calorie) content of the diet.
Moreover, dietary fat is, well, FAT! so its ready for storage, whereas carbohydrate and protein would have to be converted to fat before being stored as fat, a process which uses up a significant portion of the energy in the carbohydrate or protein. Simply, your body prefers not to convert protein or carbohydrate to fat; and it can't convert fat to either protein or carbohydrate.
Dietary fat does not directly promote fat oxidation and has little thermogenic potential, so it is either used as fuel or stored as body fat.8 Every gram of fat you eat reduces use of body fat by a gram; so, the more fat in your diet, the less fat you draw from fat stores and the slower you reduce stores of body fat.
Since to have the best fat loss diet you need to create a negative energy balance and a negative fat balance, restricting fat takes you directly to a lower intake of both energy and fat. No amount of ketogenic mumbo-jumbo abracadabra will change the biochemical fact.
A metabolic ward study that compared the rate of fat loss from either a low fat high carbohydrate diet or a high fat low carbohydrate diet found that, calorie for calorie, restricting dietary energy intake by a given amount via fat restriction results in more body fat loss than restricting dietary energy intake to the same degree via carbohydrate restriction. In this study, a low carbohydrate diet resulted in a loss of about 53 g of fat per day, while an equicaloric low fat diet resulted in a loss of about 89 g of fat per day (about 60% greater rate of fat loss for the low fat diet).9 A meta-analysis of 32 controlled feeding studies with isocaloric substitution of carbohydrate for fat found that both energy expenditure and fat loss were greater with low fat diets than with low carbohydrate diets.10
Another important consideration is nutrient-density of carbohydrate-rich whole foods vs that of fats. Basically, fats occurring in or added to foods are mostly empty calories, providing insignificant amounts of vitamins and minerals.
For example, as shown below, both 312 g of lean, trimmed sirloin and 200 g of untrimmed ribeye provide 500 kcal. That means that for the same kcal, you can consume a larger portion of sirloin. Moreover, the sirloin provides more protein and greater amounts of vitamins and minerals (green marks the higher values) except for vitamin D, which is in negligible amounts in either steak, the daily requirement being about 4000 IU, about 80 times what the ribeye supplies. The sirloin is significantly more nutrient-dense!
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To ensure nutrient adequacy when restricting calories for the best fat loss diet, you are better off using a nutrient dense fruit to replace the fat calories of the high fat meat, as we recommend in Meats & Sweets. For example, as shown below, 200 g of lean, trimmed sirloin steak plus 1.5 cup of orange juice supplies significantly more nutrients than 200 g untrimmed ribeye with the same energy intake (500 kcal). The sirloin plus OJ combination is especially richer in folate, vitamin C, vitamin A activity, magnesium and potassium (more than twice as much potassium!).
The best fat loss diet must be nutrient dense and meet your micronutrient needs, because significant shortfalls of critical nutrients like calcium, potassium, and all vitamins might result in excessive appetite, as your body seeks the foods it needs to get the deficient nutrients, defeating your need for a negative calorie and fat balance. Unfortunately, popular weight loss diets like South Beach, Atkins, DASH and Best Life fail to meet micronutrient requirements during negative energy balance conditions.16
The sport of bodybuilding involves reducing body fat to a minimum while maintaining muscle mass at a maximum. Therefore the sport requires participants to use the most effective fat loss diet.
In summary, for the best fat loss diet, you should combine high intensity resistance training with an energy-restricted, high protein, reduced fat diet providing 2.3-3.1 g/kg/d protein, 15-30% of calories from fat, and the remainder of calories from carbohydrate, eating 3-6 meals daily, and restricting energy (fat + carbohydrate) intake by no more than 500 calories per day to achieve gradual fat loss of no more than 1 pound per week.12
Yes, for the best fat loss diet you should keep tabs on your energy intake, also known as caloric balance. Over time (not necessarily every day) you need to establish a caloric deficit (negative energy balance). Everyone who loses weight does so by creating a negative energy and fat balance. Tracking caloric intake and expenditure with an app like Cronometer.com can help you achieve this.
If you need help designing and implementing the best fat loss diet so that you have the right energy, fat, protein, carbohydrate and micronutrient intakes, contact me for online coaching.
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2. Bergouignan A, Kealey EH, Schmidt SL, Jackman MR, Bessesen DH. Twenty-four hour total and dietary fat oxidation in lean, obese and reduced-obese adults with and without a bout of exercise. PLoS One. 2014;9(4):e94181. Published 2014 Apr 8. doi:10.1371/journal.pone.0094181 <https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3979741/>
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4. Bray GA, Smith SR, de Jonge L, Xie H, Rood J, Martin CK, Most M, Brock C, Mancuso S, Redman LM. Effect of dietary protein content on weight gain, energy expenditure, and body composition during overeating: a randomized controlled trial. JAMA. 2012 Jan 4;307(1):47-55. doi: 10.1001/jama.2011.1918. Erratum in: JAMA. 2012 Mar 14;307(10):1028. PMID: 22215165; PMCID: PMC3777747. "Among persons living in a controlled setting, calories alone account for the increase in fat; protein affected energy expenditure and storage of lean body mass, but not body fat storage."
5. Leaf A, Antonio J. The Effects of Overfeeding on Body Composition: The Role of Macronutrient Composition - A Narrative Review. Int J Exerc Sci. 2017 Dec 1;10(8):1275-1296. PMID: 29399253; PMCID: PMC5786199. "However, recent evidence suggests that there is a quantitative difference in protein versus carbohydrate and/or fat overfeeding as it relates to body composition. Protein overfeeding or the consumption of a high protein diet may not result in a gain in body weight or fat mass despite consuming calories that exceed one's normal or habitual intake. "
6. Hellerstein MK. De novo lipogenesis in humans: metabolic and regulatory aspects. Eur J Clin Nutr. 1999 Apr;53 Suppl 1:S53-65. Review. PubMed PMID: 10365981.
7. Shutz Y. Concept of fat balance in human obesity revisited with particular reference to de novo lipogenesis. Int J Obesity 2004 Dec 13; 28:S3-S11.
8. Schutz Y, Flatt JP, Jéquier E . Failure of dietary fat intake to promote fat oxidation: a factor favoring the development of obesity. Am J Clin Nutr 1989; 50: 307–314.
9. Hall KD, Bemis T, Brychta R, et al. Calorie for Calorie, Dietary Fat Restriction Results in More Body Fat Loss than Carbohydrate Restriction in People with Obesity. Cell Metab. 2015;22(3):427–436. doi:10.1016/j.cmet.2015.07.021 <https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4603544/>
10. Hall KD, Guo J. Obesity Energetics: Body Weight Regulation and the Effects of Diet Composition. Gastroenterology. 2017;152(7):1718-1727.e3. doi:10.1053/j.gastro.2017.01.052.
11. Iraki J, Fitschen P, Espinar S, Helms E. Nutrition Recommendations for Bodybuilders in the Off-Season: A Narrative Review. Sports (Basel). 2019;7(7):154. Published 2019 Jun 26. doi:10.3390/sports7070154
12. Helms ER, Aragon AA, Fitschen PJ. Evidence-based recommendations for natural bodybuilding contest preparation: nutrition and supplementation. J Int Soc Sports Nutr. 2014;11:20. Published 2014 May 12. doi:10.1186/1550-2783-11-20
13. Cotton JR, Burley VJ, Westrate JA, Blundell JE. Dietary fat and appetite: similarities and differences in the satiating effect of meals supplemented with either fat or carbohydrate. J Human Nutr Diet (1994), 7, 11-24.
14. Rising R, Alger S, Boyce V, et al. Food intake measured by an automated food-selection system: relationship to energy expenditure. Am J Clin Nutr. 1992;55(2):343–349. doi:10.1093/ajcn/55.2.343
15. Galgani J, Ravussin E. Energy metabolism, fuel selection and body weight regulation. Int J Obes (Lond). 2008;32 Suppl 7(Suppl 7):S109–S119. doi:10.1038/ijo.2008.246
16. Calton, J. (2010). Prevalence of micronutrient deficiency in popular diet plans. Journal of the International Society of Sports Nutrition, 7, 24-24.
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