How does protein help with weight loss?

For midlife women, optimising protein intake is one of the most effective and often overlooked ways to lose weight. While creating a calorie deficit is still necessary for weight loss, it doesn’t have to come from severe food restriction, starving yourself or exhausting cardio! 

In my practice, I see many women who are not happy with their weight, and most of the time I discover that they are not eating enough protein. I calculate each client's personal protein requirements and give them simple, practical strategies to reach them. It’s so rewarding when they report back to me that this simple strategy has eliminated their need for morning snacks and afternoon pick-me-ups, often leading to weight loss along the way. Only yesterday, yet another client marvelled at how her cravings for sweet and salty snacks had completely disappeared, just by making an effort to increase her protein at breakfast, lunch and dinner.

So, how does protein actually help with weight loss?

Protein balances your blood sugar

One of the main ways that protein helps with weight loss is by balancing blood sugar. When we eat carbohydrates - especially refined carbs - we experience a fairly rapid blood sugar spike which is quickly followed by a crash. This crash is generally accompanied by fatigue, irritability and cravings for more sugar. This is why people who eat sugary processed cereals or white toast for breakfast often find themselves reaching for cookies or soft drink mid-morning - neither of which are particularly helpful on the weight loss front! In contrast, when we eat protein, our blood sugar remains much more stable, leading to steady energy, better mood and fewer cravings.

Insulin resistance is a significant contributor to weight gain in midlife women. As oestrogen levels decline during perimenopause and menopause, our cells naturally become less sensitive to insulin, and diets high in refined carbohydrates can make this worse by keeping blood glucose consistently elevated. Over time, this means glucose stays in the bloodstream rather than being used efficiently by our cells, and the resulting higher insulin levels encourage the body to store more fat, especially around the midsection.This is exactly why keeping blood sugar stable through adequate protein intake matters so much in midlife, as it prevents the glucose spikes that drive this cycle in the first place.

Protein keeps you feeling full for longer

Protein supports the hormones that regulate hunger and fullness. Ghrelin is often called our hunger hormone as it rises before we eat and prompts us to look for food, then falls again once we’ve had enough. Eating adequate protein has been shown to suppress ghrelin more effectively than carbohydrates or fat, meaning that nagging hungry feeling settles more quickly. At the same time, protein triggers the release of GLP-1, and other fullness hormones in the gut, which signal to the brain that we’ve had enough and to slow down how quickly food moves through our system. Together, this means a protein-rich meal keeps us satisfied for longer, making it much easier to avoid the mindless snacking that can work against weight loss.

Protein has the highest thermic effect of food of the three macronutrients. 

Thermic energy refers to the energy our bodies use simply digesting, absorbing and processing what we eat, and it varies quite a bit depending on what’s on our plate. Digesting and metabolising protein burns roughly 20 to 30 percent of its own calories, compared to just 5 to 10 percent for carbohydrates and next to nothing for fat. In practical terms, if you eat 100 calories worth of protein, your body might use 20 to 30 of those calories just processing it, whereas the same 100 calories from carbohydrates would only use 5 to 10. This is not going to be the single factor that determines whether you lose weight, but over the course of a week, those extra calories burned from protein add up and certainly help you move in the right direction.

An added benefit: Protein helps preserve your muscle during weight loss

Weight loss still requires being in an energy deficit somewhere along the line, and when women are in any kind of energy deficit, the body will burn muscle along with fat unless there’s enough protein to protect it. This matters more in midlife because oestrogen decline already accelerates muscle loss and muscle is what drives resting metabolic rate (the calories you burn at rest, which make up the majority of what you burn each day, therefore a higher rate means you are burning more calories without doing anything extra)

While GLP-1 medications have proven remarkably effective for weight loss, what is less talked about is that a significant portion of the weight lost on these medications is lean muscle rather than fat. This makes prioritising protein even more important for anyone using these medications, since adequate intake is one of the most effective ways to protect muscle mass while the weight comes off.

A final word…

Just as the amount of protein you eat matters, so does where it comes from. I’m concerned about the fact that food manufacturers have jumped on the protein bandwagon and are now slapping “high protein” labels on virtually everything. As much as I think people (especially midlife women) need to be making sure they are eating enough protein, I’d prefer that they get it from “real food” sources (like fish, poultry, eggs, legumes, tofu and dairy), rather than ultra-processed products.

References

Leidy, H. J., Carnell, N. S., Mattes, R. D., & Campbell, W. W. (2007). Higher protein intake preserves lean mass and satiety with weight loss in pre-obese and obese women. Obesity (Silver Spring, Md.), 15(2), 421–429. https://doi.org/10.1038/oby.2007.531

Sargeant, J. A., Henson, J., King, J. A., Yates, T., Khunti, K., & Davies, M. J. (2019). A Review of the Effects of Glucagon-Like Peptide-1 Receptor Agonists and Sodium-Glucose Cotransporter 2 Inhibitors on Lean Body Mass in Humans. Endocrinology and metabolism (Seoul, Korea), 34(3), 247–262. https://doi.org/10.3803/EnM.2019.34.3.247

Suba Z. (2012). Interplay between insulin resistance and estrogen deficiency as co- activators in carcinogenesis. Pathology oncology research : POR, 18(2), 123–133. https://doi.org/10.1007/s12253-011-9466-8

van der Klaauw, A.A., Keogh, J.M., Henning, E., Trowse, V.M., Dhillo, W.S., Ghatei, M.A. and Farooqi, I.S. (2013), High protein intake stimulates postprandial GLP1 and PYY release. Obesity, 21: 1602-1607. https://doi.org/10.1002/oby.20154

Westerterp, K. R. (2004). Diet induced thermogenesis. Nutrition & Metabolism, 1(1), 1-5. https://doi.org/10.1186/1743-7075-1-5

Wolever, T. M., Zurbau, A., Koecher, K., & Au-Yeung, F. (2024). The Effect of Adding Protein to a Carbohydrate Meal on Postprandial Glucose and Insulin Responses: A Systematic Review and Meta-Analysis of Acute Controlled Feeding Trials. The Journal of nutrition, 154(9), 2640–2654. https://doi.org/10.1016/j.tjnut.2024.07.011