High Protein Diet Induces Sustained Reduction in Ad Libitum Intake Despite Diurnal Leptin Compensation

I've written several hundred posts on this blog.  There are some, especially from early on in 2010, that I would really like my readers to see, and I sure don't expect folks who are just finding this blog now to go back and read everything to find some that I feel are key.  I refer to this study quite often because I think for those finding themselves gaining a little bit each year and not wanting to hop on some "diet rollercoaster", there is merit to -- especially for us women -- upping the protein as a percentage in the diet.  So when I was compiling graphics for the 24 Hour Leptin Profiles post, this study was the first I knew to go to for a graphic.  So, I'm bumping the original, adding a little emphasis to the text but not changing it, and I'll add some commentary on leptin at the end.  

Original Publish Date:  4/30/10

Background: Ad libitum, low-carbohydrate diets decrease caloric intake and cause weight loss. It is unclear whether these effects are due to the reduced carbohydrate content of such diets or to their associated increase in protein intake.

Objective: We tested the hypothesis that increasing the protein content while maintaining the carbohydrate content of the diet lowers body weight by decreasing appetite and spontaneous caloric intake.

Design: Appetite, caloric intake, body weight, and fat mass were measured in 19 subjects placed sequentially on the following diets: a weight-maintaining diet (15% protein, 35% fat, and 50% carbohydrate) for 2 wk, an isocaloric diet (30% protein, 20% fat, and 50% carbohydrate) for 2 wk, and an ad libitum diet (30% protein, 20% fat, and 50% carbohydrate) for 12 wk. Blood was sampled frequently at the end of each diet phase to measure the area under the plasma concentration versus time curve (AUC) for insulin, leptin, and ghrelin.

Results: Satiety was markedly increased with the isocaloric high-protein diet despite an unchanged leptin AUC. Mean (±SE) spontaneous energy intake decreased by 441 ± 63 kcal/d, body weight decreased by 4.9 ± 0.5 kg, and fat mass decreased by 3.7 ± 0.4 kg with the ad libitum, high-protein diet, despite a significantly decreased leptin AUC and increased ghrelin AUC.

Conclusions: An increase in dietary protein from 15% to 30% of energy at a constant carbohydrate intake produces a sustained decrease in ad libitum caloric intake that may be mediated by increased central nervous system leptin sensitivity and results in significant weight loss. This anorexic effect of protein may contribute to the weight loss produced by low-carbohydrate diets.

My Summary:

Subjects:  19 Adults, mostly Women (16), starting data provides Mean ± Std.Dev
  • Weight (kg): 72± 8.9 (56.1–88.3) 
  • BMI (kg/m2) : 26.2 ± 2.1  This is moderately overweight 
  • Subjects were weight stable for ≥3 mo before the study, and were at their lifetime maximal weight.
  • Subjects were healthy and excluded were anyone with a BMI over 30, smokers, regular exercisers, high alcohol consumption, pregnancy, diabetes, and anyone regularly consuming a regular diet of less than 35% or over 55% carb.
The subjects were told this was NOT A WEIGHT LOSS study and they were not to expect to lose weight.  I think this is important, because the weight loss experienced during the ad libitum phase was accomplished without even "trying".

Study phases:  
  • 2 Weeks CRC1:  Weight maintaining calorie controlled diet - 15% Protein / 50% Carb / 35% Fat
  • 2 Weeks CRC2:  Weight maintaining calorie controlled diet - 30% Protein / 50% Carb / 20% Fat
  • 12 Weeks CRC3:  Ad Libitum High Protein  - 30% Protein / 50% Carb / 20% Fat
Essentially this study replaced fat with protein controlling carb content at 50%.  Weight was maintained during the first 4 weeks by maintaining calorie balance.  Simply replacing fat with protein didn't result in any weight loss for constant caloric intake, but greatly improved reported appetite/satiety.

However, when allowed more variety, and provided with about 15% excess food, and counseled not to deliberately change anything just eating to fullness, the study participants spontaneously decreased caloric consumption by ~440 cal/day.  Remember ... these participants didn't think they were even participating in a weight loss study and weren't trying to lose weight.  So even with insulin coursing through their veins, they lost an average of 10.8 lbs in 12 weeks.  

Some Energy Balance Math:  
Caloric Deficit:  440 cal/day * 7 days/week * 12 weeks = 36,960 total average caloric restriction
Caloric Equivalent of Pounds Lost:  10.8 * 3500 cal/pound = 37,800 calories

So as the authors state, the weight loss is in accordance with the spontaneous reduction in calories.  Interestingly enough they did not see demonstrable changes in TEF/RMR from the higher protein content.

*** EDIT:  Not all weight was fat, indeed of 4.9 kg (10.8 lbs) of weight loss, roughly three-fourths was fat mass of 3.7 kg = 8.1 lbs.  So the calc may differ slightly from predicted.  ***

This study demonstrated that when the participants didn't really know the composition of their diets or that they were "on a diet", ate considerably less of a LOW FAT (only 20%) diet when protein content as a percent of intake was doubled.

The weight loss observed over 12 Weeks is comparable to that seen with LC diets.  Aside from those deliberately choosing high fat proteins and adding lots of fat on top of that, I think the 30% protein content of this diet is probably comparable to what most consume doing Atkins or similar plans "by the book".  What this study demonstrated was that an unstructured low fat high carb diet can lead to weight loss comparable to that of an unstructured low carb high fat diet.  

I do think this sort of diet might be harder to achieve w/o some sort of planning (study participants were provided with foods) than your basic LC diet.  Counting carbs will naturally increase protein content of the diet because whole meats and eggs contain relatively high percentages.  It is easier to keep carbs under some threshold (20g or 50g) which would amount to 5-10% of calories in average reducing diets and the protein has to be considerable.  However if one is shooting for 1500 calories, then 30% would be 450 calories = 112.5g protein.  If one is eating 3 meals and 2 snacks, a loosely structured plan could be accomplished by eating 30g protein at each meal and 10g protein for each snack, choosing leaner proteins and limiting added fats and eating lots of veggies and fruit, and reasonable portions of whole carbs (potatoes, brown rice, legumes, wholegrain bread).

Yet another study demonstrating that reduced caloric intake and not macronutrient composition of the diet is what results in weight loss.  No Metabolic Advantage either way was even demonstrated in this study replacing fat with protein.

New Content:  Below left are the 24 hour leptin profiles, leptin levels (top) and change in leptin levels (bottom) for CRC1 (□), CRC2 (•), and CRC3 (▵).  Below right is the table of various 24 hour leptin assessments (taken the last 24 hours of each study phase)

It's interesting that the "peak-to-nadir" (max-to-min) swing was lower on the high protein diet in both the isocaloric phase and the ad lib (spontaneous calorie reduced) phase vs. the standard diet, but the 24 hour AUC of leptin was relatively unchanged between the isocaloric diets but significantly reduced in the ad libitum phase.  The ad libitum phase lasted 3 months during which subjects lost an average of almost 11 lbs.  It is possible that this reflects an improvement in leptin sensitivity with weight loss.  However this raises more questions on how macro composition of a diet impacts leptin.  It does not appear to be have much if any impact during the postprandial phase -- I hope we can put Rosedale's notions of anything "spiking" leptin to sleep sometime soon!  But it is rather interesting to note that swapping 15% fat for 15% protein on a rather high carb diet (50%) lowers the overnight (diurnal) rise in leptin in similar fashion, independent of caloric intake.  The two leptin curves for high protein phases are almost identical, just translated vertically down after weight/intake reduction.

It does not appear that leptin has anything to do with the satiety/appetite reduction unless it is somehow impacting leptin sensitivity.  In the words of the study authors:  "The anorexic effect of dietary protein, which may be due in part to increased CNS leptin sensitivity, is apparently stronger than any orexigenic effect of increased ghrelin concentrations accompanying weight loss with a high-protein diet."Grehlin -- often associated with increased appetite, was greater in this study with increased protein!  At right is the plot of change in fat mass vs. leptin concentration for all 19 subjects (note CRC2 is end of isocaloric phase, CRC3 is end of 12 weeks weight loss of avg. ~ 1 lb/week).  
These authors had previously done this experiment replacing 15% fat with carbohydrate.  The result?  A spontaneous reduction in caloric intake roughly half that seen in this current experiment.  I'll have to blog on that study sometime.  As to any sort of leptin "spike" ... or rather "pulse", from the discussion:
Havel et al (32) reported that substitution of carbohydrate for dietary fat increased the diurnal circulating leptin pulse amplitude (peak minus nadir plasma leptin concentration). These authors speculated that, as for other endocrine systems (33,34), the CNS might interpret an increase in leptin pulse amplitude as a signal calling for a decrease in appetite independently from any change in the integrated circulating leptin concentration (32). Our data directly address this hypothesis because we observed a decrease in leptin pulse amplitude between visit CRC1 and visit CRC2 (decreased peak minus nadir plasma leptin concentration and decreased AUC of the change in leptin) without a significant change in integrated circulating leptin concentration (leptin AUC). The subjects reported a marked increase in satiety despite this isolated reduction in leptin pulse amplitude. These data suggest that if diurnal leptin pulse amplitude is a signal regulating energy balance, it is less important than the putative change in CNS leptin sensitivity observed in the present study.
I would note, insulin AUC was increased for the high protein phases, and yet the participants lost significant weight they were not to expect to lose when allowed to "eat as much as they wanted".   More TWICHOO* busting stuff!  But according to Gary, we've been duped into thinking protein is satiating ... it's fat that is!  This study says otherwise.

*Taubes Wrong Insulin Carbohydrate Hypothesis Of Obesity


Unknown said…
Hi Carbsane:
I am putting myself through this study, informally. I have neither lost or gained weight in the past 3 months since I went off Optimal (Kwasniewki) and LC, due to the relative inconvenience of that woe while moving to Yukon and tent-camping with 2 kids in the process.
Now I'm trying to prove the alternate hypothesis (to LC wisdom) that a lower fat (25%), high protein (30%) and mod carb (45%) intake will curb my intake enough to get another 2 or 3 inches off the waist. I won't count calories; eat ad libitum of leaner meat, baked potatoes, rice, veggies, fruit; and go lightly on added fats. I'll report periodically.

CarbSane said…
I look forward to your report! After Labor Day (and the ensuing festivities), I too plan to make another weight loss attempt that I'll report on the other blog. Please do check back and let me know how this works for you. I've been doing more moderate carbs for most of the summer and holding steady. Admittedly I've been relaxed on foods and eating in general (a bit less mindful of intake). Summer is a time for lots of social occasions, and this one I decided after a while that maintaining would be success. Mission accomplished!
Unknown said…
Hi Carbsane and fellow readers:

It's been over 2 weeks and I think a casual report would be worthwhile.
I've noticed a consistent, slight decrease in food intake. I would say this is mostly in the form of no food cravings to satisfy after dinner and nighttime.
I haven't noticed any major shrinkage around the midsection (and don't have a measuring tape to verify) but subjectively feel that there's less to grab there. I think given another 8-10 weeks, I'll see stronger signs of fat loss.

Eating a lot of protein has not been that difficult. Keeping it always low-fat (< 25%)is more challenging because 60g of fat per day is easily obtained from the meat, eggs, a bit of coffee cream. Eating a few oz cheese on a given day can add another 10% fat for that day, but I believe in cheese for the calcium I need. I've changed my cooking method to render out more fat but keep it edible (e.g. braising; rinsing cooked ground beef with hot water). It's been nice to have more freedom around carbs, and it's mostly taken in whole form like baked potato, peas, rice, fruit. But there is some use of sugary condiments like chili sauce. I would not recommend my higher carb levels to diabetic people. Since I'm not diabetic I'm not worried about taking in 40-45% needs as carbs.

CarbSane said…
Thanks for the update! Sounds like you're doing well. FWIW, the LoBAG-40 (40% carb) diet improved blood sugars in untreated diabetics. Stay away from too much sugar and you'll be fine. The fat can add up, but so long as most of that comes from whole foods I think you should be OK. It's the junk and lots of added fats that will get you in trouble. I consume a fair amount of lower fat dairy -- no not the 0% fake stuff, just reduced fat real cheeses and, Breakstone 2% Cottage Cheese. You're coming off a stint doing high fat OD so this has no doubt been quite an adjustment for you. This study was rather low fat at 20%. For "us", 30%-40% is low fat!

So are you basically counting grams of each macro?

Keep us posted :)
Unknown said…
The macro I actively track is fat grams because I'm trying to keep it around 25%. I know food charts can only give average content so I don't get hung up on knowing exact fat content of meat. To keep fat lower, I'm not taking in nuts, 90% chocolate, or veg oils (using only vinegar on salads)right now. Interestingly, I don't miss those items yet; and I use milk to whiten my Americano's.

With protein tracking, I use a rule of thumb: 50g protein per 7 oz trimmed and cooked red meat. Since I don't have a kitchen scale, I use the visual gauge 'one deck of cards'= 3.5 oz meat. I use the food label data for canned fish, eggs, cheese.

With carbs, at this point I won't track to control. I'm counting on the anorectic effect of high protein to keep those carbs where they need to be. If there's no noticeable weight loss by week 8, then I'll reconsider.

I might be one of those oddities who cheat by going LC OD, as a break from my usual LF high-carb !
CarbSane said…
One of the limitations trying to apply this "ad libitum" in real life is that the participants were provided with food that presumably averaged the desired macronutrient target %'s. In order to do so they had to go with leaner meats, etc. It would be interesting to note if they counseled the participants on making sure to eat roughly in the same percents in the ad lib phase, or if there was a prescription to keep the protein intake up (choose those foods first) -- IOW, if they were provided with 15% excess foods and they spontaneously ingested almost 20% less on the ad lib, that's a pretty big swing. A participant could potentially consume a diet with a macronutrient distribution that differed considerably from the 30/20/50 P/F/C. It would have been nice to get a breakdown of the actual intake ratios in the ad lib phase rather than just the calories. I wonder if they ate less protein and fat (on a gram basis).

Here's where I think diets like Zone tend to be difficult to implement.
Unknown said…
Yep, I don't think I'm maintaining the original ratio (except for protein close to 30%) on my way down or when I arrive. I predict my ratios will be closer to Primal Blueprint: I can't see cutting fat below 60g/day so that means fat will account for 35-40% intake a day, then carbs will account for another 35% (primal's ceiling being 600 carb kcals/day).

My guess is that the study participants were counselled to maintain their protein levels by way of being told 'try not to purposely change' what they eat when going from the macro-controlled to the ad lib phase. At this point, I have to deliberately eat more protein when I'd rather put more baked potato/rice on my plate and take less meat. But as I stated earlier, it's not that difficult, esp. knowing that the extra protein is my 'med' against overeating.

Have a great weekend,
Diana said…
I do wonder whether the mere fact of being watched, and therefore conscious of what one eats, results in a reduction of caloric intake. This also demonstrates the value of food journaling.

In any case, another piece of data proving that negative energy balance is the heart of the matter.
Thomas T said…
"Caloric Deficit: 440 cal/day * 7 days/week * 12 weeks = 36,960 total average caloric restriction
Caloric Equivalent of Pounds Lost: 10.8 * 3500 cal/pound = 37,800 calories"

I am always a bit weary about the 3500 figure... isn't it usually for fat mass? The study listed 4.9kg WEIGHT loss and 3.7kg FAT loss, so wouldn't it be 3.7 * 0.8 * 1000 * 9 = 26640 caloric deficit for the fat (80% fat in fat tissue, 1000 grams in 1kg, 9 calories per gram of fat) and for the extra 1.2, a LOT of it would be water, so let's say 75% water, 25% muscle (crude, but lets say that 25% is pure protein and disregard lipid content), so let's say 1.2 * 0.25 * 1000 * 4 = 1200(1.2kg, 25% protein, 1000 grams per kg, 4 calories per gram of protein)

So total = 26640 + 1200 = 27840 calories?
Sanjeev said…
> I am always a bit weary about the 3500
> figure... isn't it usually for fat mass?

NIH researcher Kevin Hall's answer:


(needs Java to run)
This simulator gives you an idea of what exercise and caloric intake do. I just use it to get an idea of what deltas do since I don't know what parameters are at work in the code & how they can vary with the individual

For fun, set up a scenario and simulate it, then change the carbohydrate percentage and watch body fat % level in the "view tabular data" area.

Sanjeev said…
Maybe a US citizen/resident could get the source code & post it?

Hall supposedly at one point had a spreadsheet available but I don't see it at the moment.
CarbSane said…
Hi Thomas T, Presuming you're a different Thomas, Welcome to the Asylum! Yeah, I've addressed the 3500 figure here before and see it mostly as a rule of thumb. Using your calcs, it could be said that the caloric deficit more than accounted for the losses.

" We found that RMR, the major component of total daily energy expenditure, did not increase with the high-protein diets and that overall weight loss during ad libitum feeding was fully explained by the cumulative reduction in caloric intake. Thus, with the use of real food items and the natural feeding conditions used in the present study, increased thermogenesis did not appear to contribute significantly to the observed weight loss."

Doesn't appear they measured RMR. Likely it was depressed by 12 weeks energy intake reduction.
CarbSane said…
Interesting Diana, For the carb for fat sister study, it would be nice to have this same scenario repeated with one more manipulation: Replace 15% carb with fat at 15% protein, and see if there's a spontaneous reduction in intake. My hunch is this wouldn't occur, but that's just a hunch, as 35% carb is still enough to include all favorite foods including carbs as fat-calorie-vehicles, and the the higher volume of food would decrease. My prediction would be either no change in intake or even a slight increase due to eating amounts vs. calories. This would explain the ~200 cal deficit switching fat for carb. The spontaneous deficit on the high protein diet, however, was significantly greater than that on high protein ... so I do think this illustrates the protein effect. I've got to look at the other study in more depth.
Jenigma said…
I had the same thought as Diana and would like to know if there are any similar studies that has the reverse order of the (2 week) study phases.
genius786 said…
Thanx for Sharing your knowledge.. Thumbs up!

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