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A high-protein diet for weight loss

Clinical review pending

Protein can help you feel full and preserve muscle while losing weight. Which amounts are worth considering, and where studies, kidney health and personal circumstances set limits.

How much protein helps with weight loss? A high-protein diet can keep you full for longer and help preserve muscle mass. Whether your weight goes down also depends on your total energy intake. How much protein makes sense depends on your personal circumstances.

It pays to ask more precise questions here: How much is enough, and when does it become too much? Does protein directly support fat loss, or does it mainly help you feel less hungry? Research looks at these questions separately. The answers explain what a high-protein diet can do and why a single recommended amount does not suit everyone.

How protein affects energy expenditure

To digest, absorb and process protein, the body needs more energy than it does for carbohydrates or fat. For protein, this so-called thermic effect of food comes to roughly 20 to 30 percent of the protein energy consumed. For carbohydrates it is about 5 to 10 percent, and for fat only 0 to 3 percent. So a larger share of the energy in protein is used up just processing it and is then no longer available for other bodily functions or as an energy reserve. During a calorie deficit, this effect can support weight loss without necessarily requiring you to eat less food. See the reviews by Halton and Hu and Calcagno et al..

How much does this difference add up to over time? Getting 25 to 30 percent of total calories from protein could raise daily energy expenditure compared with a lower-protein diet, even at the same calorie intake. A difference like that could accumulate over time. It remains unclear, however, whether the evidence cited here, from Guarneiri et al., supports higher expenditure at rest and across the whole day in addition to the energy spent on digestion. According to its title, the review covers diet-induced thermogenesis, and the specific figure of 25 to 30 percent cannot yet be reliably traced to it either.

Protein may also influence how blood sugar responds after a meal. One proposed explanation is that glucose is absorbed more slowly, insulin spikes are smaller and blood sugar stays more even. That could reduce sharp drops in blood sugar and the hunger or cravings that come with them. This chain of effects is not backed by a source here, however. Protein can itself stimulate insulin release; the response depends on factors such as the protein source and the makeup of the meal.

Insulin promotes the uptake of glucose into cells and inhibits the breakdown of fat. This leads to the assumption that at moderate insulin levels the body might find it easier to use stored fat as an energy source. A moderate insulin level alone does not guarantee any loss of body fat, though. No general effect of high-protein meals on fat loss can therefore be derived from these individual processes.

How protein affects appetite, hormones and muscle

How gut hormones contribute to fullness

Protein stimulates the release of satiety hormones in the gut, including GLP-1, CCK and PYY. They send signals to the brain that contribute to a feeling of fullness. Ghrelin, a hormone that promotes hunger, can also respond to protein intake. A falling ghrelin concentration is a possible additional explanation for reduced hunger, but it cannot be taken for granted across the board. Short-term and longer-term hormone responses also need to be kept apart.

These processes can make it easier to stick to a calorie deficit without constantly feeling restricted in what you eat. In the studies cited, people with a higher protein intake reported less hunger or spontaneously ate fewer calories without consciously limiting their food intake. See Weigle et al. and Kohanmoo et al.. Weigle et al. state right in their title that food intake fell despite compensatory changes in leptin and ghrelin concentrations. Less hunger therefore cannot simply be equated with lasting suppression of ghrelin.

Preserving muscle mass while losing weight

When you lose weight, you can lose muscle mass as well as fat. Protein supplies the amino acids that muscles need for repair and maintenance. Getting enough of it during a calorie-reduced diet can therefore limit muscle loss. That way, a larger share of the weight lost can come from fat mass.

A range of 1.6 to 2.2 grams of protein per kilogram of body weight per day is given as a guide for preserving muscle. Whether this generally preserves considerably more lean mass during weight loss than a lower intake cannot be derived directly from the work cited here: according to its title, Morton et al. looks at protein supplementation and the gains in muscle and strength from resistance training in healthy adults. Hector and Phillips deals with weight loss in elite athletes. How well these results carry over to other groups and to exactly this range of amounts remains an open question.

Preserving muscle also matters for energy expenditure. Muscle tissue uses more energy at rest than fat tissue. If more muscle mass is preserved, that can help sustain energy expenditure during weight loss.

How energy expenditure adapts during weight loss

When fewer calories are available, the body adapts in part by using less energy. That can make further weight loss harder. A higher protein intake might soften this adaptation, because processing protein takes energy and protein can help preserve metabolically active muscle mass. Effects on thyroid and other metabolic hormones are put forward as a further explanation, but no source is given for this here.

On this assumption, protein would not prevent the adaptation entirely but might limit how large it is. Further fat loss might then be possible without cutting calorie intake to a level that is hard to sustain in the long run. How strongly protein actually affects this so-called adaptive thermogenesis, and what role hormonal changes play in it, is not settled by the sources cited. Such an effect therefore cannot be expected for every person.

What determines the effect of protein on weight loss

How much protein, and from which sources?

For fat loss, a higher range of 1.6 to 2.7 grams of protein per kilogram of body weight per day is also mentioned. Higher amounts might be particularly helpful with a larger calorie deficit or regular resistance training. The evidence cited for this, Morton et al., however, looks at gains in muscle and strength from resistance training and does not directly answer the question of this range for fat loss.

The range of 1.6 to 2.7 grams therefore cannot be treated as a general recommendation. Its upper limit is also above the 2.2 grams mentioned earlier; who the higher amount is meant for and what it is based on remain unclear. A protein calculator for muscle building can take body weight, activity level and goals into account and derive a personal guide value from them. Such a calculation does not, however, resolve the open questions about the right target group and the scientific basis of the chosen range.

Besides the amount, it matters which amino acids a protein source provides. Complete proteins contain all the essential amino acids in sufficient amounts. They can support the building of muscle protein, known as muscle protein synthesis, more effectively than a source in which some essential amino acids are too scarce relative to need.

Meat, fish, eggs and dairy products provide complete proteins. In plant sources such as legumes, grains and nuts, at least one essential amino acid is often present in smaller amounts. Different sources can be combined, though, so that together they supply all the essential amino acids. Leucine is especially important for stimulating muscle protein synthesis. That is why leucine-rich foods such as whey protein, chicken and beef are often highlighted in high-protein meal plans.

Spreading protein across the day

How can you divide your daily protein across meals? One possible approach is to eat roughly the same amount of protein at three to four meals instead of taking in most of it at once. Several protein-rich meals might repeatedly support the building or maintenance of muscle protein even during a calorie deficit, and so help preserve lean mass.

At least 20 to 30 grams of protein per meal is given as a guide for a sufficient muscle-building stimulus. This cannot be turned into a universal minimum threshold of 20 to 30 grams, however: the right amount depends on body size, age, protein source and the meal, among other things. Nor can a distribution be named that maximizes muscle protein synthesis in everyone. The review linked here, by Hudson et al., deals with protein distribution and muscle-related outcomes. Whether it supports the specific amount and distribution in this form remains an open question.

Why protein needs differ from person to person

Even with the same protein intake, people can lose fat at different rates, feel different levels of hunger or preserve different amounts of muscle mass. Genetic differences can contribute to this. Among other things, they affect how the body processes nutrients, responds to satiety signals and builds or breaks down muscle mass. Variants of the FTO gene have been linked to appetite regulation and fat storage. Genes that influence muscle fiber types and the rate of protein synthesis might also help determine how well muscle mass is preserved during weight loss. They do not explain the course of weight loss on their own.

How much muscle and fat mass you start with also plays a role. People with more muscle mass usually need more protein to preserve it during a calorie deficit. When body fat is already low, the need relative to body weight can also be higher. With smaller fat reserves, an inadequate protein intake can increase the risk of muscle loss.

Activity and training status come into it too. Resistance training increases both the breakdown and the building of muscle protein. That makes enough protein more important for supporting a positive protein balance, meaning more muscle protein is built than broken down. Endurance training can also increase protein needs. The assumption that this increase is smaller than with resistance training is not placed in context by a source here.

Protein metabolism changes with age. Older adults can develop what is called anabolic resistance: their muscles respond less strongly to protein and resistance training than those of younger people. For adults over 65, a possible benefit from about 1.2 to 1.5 grams of protein per kilogram of body weight per day under normal conditions has been described. Nowson and O’Connell is cited for this. This range concerns a different context from the weight-loss figures given earlier. The 1.2 to 1.5 grams should therefore not be read as the upper end of those higher ranges. The right amount for older people also depends on their state of health.

With insulin resistance or type 2 diabetes, there is also the question of whether a higher-protein diet improves blood sugar control and fat loss more often or more strongly than in people with normal insulin sensitivity. The explanation offered for such a difference is a stronger effect on insulin and glucose metabolism that is already disturbed. No scientific reference is given here for this comparison or its explanation. A stronger effect in these groups is therefore not established; metabolic health nonetheless remains a possible influence on how someone responds to a higher protein intake.

Watching changes over time

A single number on the scale says little about whether a high-protein diet is having the desired effect. Water retention, how full the glycogen stores are and the contents of the digestive tract make weight fluctuate from day to day. The trend over weeks and months tells you more, supplemented by changes in body composition and, where relevant, metabolic markers.

Waist circumference and comparison photos can make changes visible over time, but they do not measure fat mass and muscle mass separately. DEXA and bioelectrical impedance analysis are used to estimate fat mass and lean mass. Both have measurement limits, especially bioelectrical impedance analysis.

The waist-to-hip ratio can also hint at a change in fat distribution. It cannot directly prove that visceral fat has been lost, however. This fat sits in the abdominal cavity around the organs and is associated with increased metabolic risks.

Metabolic markers can add to what weight and body composition show. Fasting insulin and hemoglobin A1c, or HbA1c for short, can help assess glucose metabolism. Triglycerides and HDL cholesterol provide information about fat metabolism. High-sensitivity C-reactive protein, or hs-CRP for short, is a marker of inflammatory processes in the body. Such values may improve even before bigger changes show up on the scale. That can point to a change in metabolic health. On its own, however, it establishes neither the effectiveness of a particular way of eating nor a causal effect of the higher protein intake.

The amount of protein you actually eat is not always easy to judge, either. There is no scientific source for the specific claim that most people often underestimate it by 20 to 30 percent. A kitchen scale and a nutrition app used for a few weeks can help you judge portion sizes better and compare what you eat with your target.

Hunger and energy levels provide additional, if subjective, information. Persistent hunger, exhaustion or a loss of strength in training despite adequate protein intake can be signs that the calorie deficit is too large.

When biomarkers can help with adjustments

When there is a relevant medical question, repeated measurements of fasting insulin, leptin, thyroid values and testosterone can provide additional information. Whether they reveal improvements in metabolic health on a high-protein diet or a need for adjustment depends on the individual value, the health context and expert interpretation. Independent scientific evidence for the usefulness of this particular set of tests as an accompanying check on a high-protein diet is lacking here.

Creatinine and blood urea nitrogen, also called BUN, can help assess kidney function and nitrogen metabolism, respectively. Individual values within the reference range do not confirm, however, that the kidneys can handle a higher protein intake without problems. They do not reliably rule out kidney disease or possible problems.

With a suitable clinical question, ferritin and vitamin B12 can help assess nutrient status. That can be particularly relevant if certain food groups have been cut back. These two measurements do not provide comprehensive protection against developing deficiencies: they cannot rule out other nutrient deficiencies.

Test results that have been interpreted by a professional can complement subjective observations and support targeted adjustments. They do not, however, allow a demonstrably accurate record of every bodily response, or precise control of weight loss. Which values make sense and what changes in them mean has to follow from the specific medical question.

Frequently asked questions

How much protein should I eat each day to lose weight?

One guide range given for losing fat while preserving as much muscle as possible is 1.6 to 2.2 grams of protein per kilogram of body weight per day. The literature cited here cannot simply be applied to this entire range and to all target groups, however. For a person weighing 70 kilograms, that would be roughly 112 to 154 grams a day.

With a larger calorie deficit or regular resistance training, the upper end of this range may be worth considering. A protein calculator for muscle building can derive a guide value from body weight, activity level and goals. How appropriate that value is still depends on the basis it is calculated from and which group of people that basis applies to.

Can too much protein prevent weight loss?

Protein in itself does not prevent fat loss. What matters is total calorie intake: if extra protein leads to a lasting calorie surplus, no weight loss can be expected from it, regardless of how the macronutrients are split. The comparatively high thermic effect and the filling effect can, however, make it easier to limit energy intake.

As a result, overeating might be less likely on a high-protein diet than on a diet richer in carbohydrates or fat. For any individual, that is no guarantee of taking in fewer calories.

Is a high-protein diet safe for the kidneys?

For healthy adults, up to roughly 2.0 grams of protein per kilogram of body weight per day appears to have no adverse effects on kidney function, according to the research cited here. Most studies of this amount lasted six months at most, however. “Devries et al., 2018” is given as the source; the full reference and an associated evidence link are missing, so this statement cannot be checked here.

No unrestricted long-term safety can be derived from this. The blanket claim that a high protein intake causes no kidney damage in healthy people with normal kidney function also goes further than the basis described here. Results for roughly 2.0 grams also do not cover the amounts of up to 2.7 grams mentioned earlier.

If you have existing kidney disease, a substantial increase in protein intake should be discussed with a doctor beforehand. When kidney function is impaired, processing or excreting the additional nitrogen-containing metabolic products can be a problem.

Do I need protein powder, or is regular food enough?

Meat, fish, eggs, dairy products and legumes can cover your entire protein needs. Protein powder delivers protein in concentrated form and can be a practical way to reach higher targets, for example when you are short on time or have little appetite. Whey protein is absorbed relatively quickly and contains a lot of leucine. That can help it support recovery after training. It is not necessary for that, though.

How does the timing of protein intake affect weight loss?

Your total daily protein intake matters more than exactly when you eat it. Spread across three to four meals, protein can support muscle protein synthesis throughout the day. The at least 20 to 30 grams per meal mentioned for this is a guide value for a sufficient muscle-building stimulus, not a universal minimum. Body size, age, protein source and the makeup of the meal all affect which amount is right.

Protein shortly after resistance training can support recovery. The added benefit of this timing is considered rather small, however, compared with reaching your total daily amount.

Will I lose muscle if I don’t eat enough protein while losing weight?

Too little protein can increase the risk of muscle loss. During a calorie deficit, the body can break down muscle tissue as well as fat. Enough protein supplies amino acids for repairing and maintaining muscle and can limit this loss. That way, a larger share of the weight lost can come from fat.

Too low a protein intake, on the other hand, can encourage greater muscle loss. That can lower resting energy expenditure and make it harder to keep the weight off in the long run. More muscle loss and less fat loss are not an inevitable consequence, though. How much muscle mass is actually lost also depends on training, on the size and duration of the calorie deficit and on body composition at the start.

Can plant proteins support weight loss as well as animal proteins?

Plant proteins can effectively support weight loss. Depending on the foods you choose, this takes more careful planning. Individual essential amino acids are often present in smaller amounts relative to need. That does not mean these amino acids are missing; calling most plant proteins “incomplete” across the board is therefore inaccurate. Combining different protein sources over the course of the day helps you take in all the essential amino acids in sufficient amounts.

Many plant foods also contain less concentrated protein. Larger portions may therefore be needed for the same amount of protein. Soy, quinoa and hemp are named as complete plant protein sources that can make planning easier. The actual amount of protein per serving and its digestibility still matter for your choices.

How can I tell whether my high-protein diet is working?

The trend across several markers says more than a single weigh-in. Possible clues include strength in training that holds steady or increases, stable energy levels and less hunger between meals. A steady weight loss of 0.5 to 1 percent of body weight per week is given as a pace for losing weight. This range does not suit every person, however. An assessment of body composition can also help you judge whether you are losing fat and preserving muscle mass.

Whether a weight loss of 0.5 to 1 percent per week is appropriate depends on factors such as starting weight, state of health and risk of muscle loss. The range is therefore not a universal target.

With a suitable medical question, fasting insulin, triglycerides and high-sensitivity C-reactive protein, or hs-CRP for short, can provide objective clues to changes in metabolic health. Such changes may become visible even before noticeable weight loss. On their own, though, they do not show that the higher protein intake is responsible.

References

  • Calcagno M, Kahleova H, Alwarith J, Burgess NN, Flores RA, Busta ML, Barnard ND (2019). The Thermic Effect of Food: A Review. Journal of the American College of Nutrition, 38(6), 547-551. https://doi.org/10.1080/07315724.2018.1552544 PubMed

  • Halton TL, Hu FB (2004). The effects of high protein diets on thermogenesis, satiety and weight loss: a critical review. Journal of the American College of Nutrition, 23(5), 373-85. https://doi.org/10.1080/07315724.2004.10719381 PubMed

  • Guarneiri LL, Adams CG, Garcia-Jackson B, Koecher K, Wilcox ML, Maki KC (2024). Effects of Varying Protein Amounts and Types on Diet-Induced Thermogenesis: A Systematic Review and Meta-Analysis. Advances in nutrition (Bethesda, Md.), 15(12), 100332. https://doi.org/10.1016/j.advnut.2024.100332 PubMed

  • Kohanmoo A, Faghih S, Akhlaghi M (2020). Effect of short- and long-term protein consumption on appetite and appetite-regulating gastrointestinal hormones, a systematic review and meta-analysis of randomized controlled trials. Physiology & behavior, 226, 113123. https://doi.org/10.1016/j.physbeh.2020.113123 PubMed

  • Weigle DS, Breen PA, Matthys CC, Callahan HS, Meeuws KE, Burden VR, Purnell JQ (2005). A high-protein diet induces sustained reductions in appetite, ad libitum caloric intake, and body weight despite compensatory changes in diurnal plasma leptin and ghrelin concentrations. The American journal of clinical nutrition, 82(1), 41-8. https://doi.org/10.1093/ajcn.82.1.41 PubMed

  • Hector AJ, Phillips SM (2018). Protein Recommendations for Weight Loss in Elite Athletes: A Focus on Body Composition and Performance. International journal of sport nutrition and exercise metabolism, 28(2), 170-177. https://doi.org/10.1123/ijsnem.2017-0273 PubMed

  • Morton RW, Murphy KT, McKellar SR, Schoenfeld BJ, Henselmans M, Helms E, Aragon AA, Devries MC, Banfield L, Krieger JW, Phillips SM (2018). A systematic review, meta-analysis and meta-regression of the effect of protein supplementation on resistance training-induced gains in muscle mass and strength in healthy adults. British journal of sports medicine, 52(6), 376-384. https://doi.org/10.1136/bjsports-2017-097608 PubMed

  • Hudson JL, Iii REB, Campbell WW (2020). Protein Distribution and Muscle-Related Outcomes: Does the Evidence Support the Concept?. Nutrients, 12(5). https://doi.org/10.3390/nu12051441 PubMed; full text at PubMed Central linked in the article

  • Nowson C, O’Connell S (2015). Protein Requirements and Recommendations for Older People: A Review. Nutrients, 7(8), 6874-99. https://doi.org/10.3390/nu7085311 PubMed

Bibliographic note: For “Devries et al., 2018” in the FAQ on kidney safety, the full reference and the evidence link are missing; how it relates to the statement is unresolved.