The concept of someone going on a diet, in my eyes, is strictly to get rid of or lose body fat (almost always). The question I posted in the previous blog was: Will a low or high carbohydrate diet cause different amounts of fat loss? In general, the answer is NO.

BUT...that does not mean you should automatically choose to diet and cut out any Calories, because what you eat will have an impact on your overall health, and maybe even increase your susceptibility to gain or lose fat.

Let me explain.

The idea of someone maintaining a stable weight (fat mass) has been shown to not really depend on the type of Calories they eat, but rather more about maintaing energy balance (related to fat mass). See the following paper: Leibel, 1992;55,Clin Nutr
Basically, they looked at people (26 of them) who were kept at a stable weight for an average of 64 days. During this time they fed random diets (all the same Calories) but with different amounts of fat and carb (e.g., 15% carb/70% fat for  39 days, then switch to 15% carb/70% fat for 44 days) all the while maintaining the person's weight. Whatever combo of switching from high carb to high fat or vice versus they were able to feed similar Calories on either diet and keep weight stable.
The key point here is that variations in your day to day diet (more fat, less fat, more protein, etc.) will probably not change your weight. HOWEVER, weight and fat are not everything, as different diets can have different impacts on your health.

To lose fat you generally have to cause a Calorie deficit (aka eating significantly less in order to physically remove fat)
The type of Calories you are eating when losing body fat will probably not change how much or how little total body fat you lose, BUT they can determine where the fat comes from and how your health will be affected differently.

Insert: Miyashita, 2004;65, Diabetes Research and Clinical Practice


22 overweight/obese type 2 diabetics (16 men, 6 women) ~52yr old underwent a restricted diet (11 in one group and 11 in the other) of either 1000 Calories/day on a lower carb diet (35% carb, 35% fat) or 1000 Calories/day on a low fat diet (62% carb, 10% fat). Protein and fiber intake was equal in both groups.

What happened after 4 weeks on the very low Calorie diet? Both groups lost similar weight (~17lbs lost), similar total fat, and had similar maintenance of muscle mass. That means almost all weight lost was fat. So they probably stuck to the diets and both saw equal weight loss.

Why is low carb better than low fat even though you lose the same total amount of fat?  
Because, these were overweight/obese diabetics and while both diets essentially reversed the high blood glucose back to normal, only on the low carb diet did they see significant improvements in fasting insulin. Also, HDL-cholesterol (which was low before the diet) stayed low in the low fat group but actually increased during weight loss on a low carb diet (possibly due to the increase in saturated fat or increased lipid flux). What was more striking and the major health reason to choose a low carb diet when losing weight, was where the fat came from. Only the low carb group saw a significant decrease in visceral fat (the very bad fat surrounding your organs). This means that both groups, when on a 1000 Calorie/ day diet lost similar amounts of fat, but the low carb group preferentially pulled more fat from the area that needed fat removed. 

Energy balance (fat mass changes) was equal on either low Calorie diet (low carb vs low fat), but the improvements in health were not. 

-Pd

The age old question in its simplest form: 1) If I overeat fat or carbohydrate do they effect changes in total fat mass differently?
2) On the flip side - Will a low or high carbohydrate diet cause different amounts of fat loss? 

The answer to both of those questions is NO. That is what good research has told us...Let me explain (regarding fat gain...fat loss will be another post).

There are many things that go into this but most studies that have properly been done, in a true controlled setting show no difference in fat mass changes whether the person was overfed or underfed with varying amounts of fat and carbohydrate.

(This post and others to come will tell you that Calories seem to determine fat mass, increased or decreased, but the type of Calories are what determine HEALTH!) Therefore, fat mass does not always determine health.

Example 1. (Horton, 1995;62.AJCN)

The Horton, 1995 study was incredible and showed exactly what I need to justify my answer above.

Randomized crossover design (meaning they used the same subjects for both interventions and randomized which intervention was given first).
9 lean and 7 obese men (18-46yr) completed 1 week of controlled weight maintenance (they were fed a stable diet that resulted in stable weight; ~35% Calories from fat...so normal diet). Next they added an additional 50% of extra Calories (50% more than total Calorie intake) in the form of either ALL fat or ALL carbohydrate for 14 days. On day 1, 7, and 14 they measured 24hr total energy expenditure and RQ (ratio of fat or carbohydrate being burned), which gave them total amount of fat and carbohydrate burned. After 14 days they had a 4 week washout to lower subject weight back towards starting weight (Kudos to the researchers). During week 4 of the washout they controlled the diet again to maintain weight stability. Then another 14 days of 50% extra Calories but with the opposite type used in phase 1 (if ALL fat before than ALL carb now, and vice versus). 

RESULTS: Fat mass change was the SAME no matter where the extra Calories came from. (This was seen in both lean and obese subjects!). On average the overfed Carb group gained 1.48 kg (~3.3lb) of fat mass, and the overfed Fat group gained 1.51 (~3.3lb) of fat mass. 

What happened to general metabolism?

Total daily energy expenditure INCREASED significantly more in the overfed carb group on days 7 and 14 but no in the overfed fat group. Why did energy expenditure go up in the carb group? To burn off the extra carbs of course. There was literally no change in the total carb or fat burning after overfeeding of fat (fat did go up slightly and carb down). 
If the overfed carb group was burning more total energy and the overfed fat group was eating more fat then why didn't we see a difference in total fat mass changes between the groups? Fat mass balance.

In the overfed carb group as carb burning dramatically increased, fat burning dramatically decreased! 

What does all this mean? Both trials were hypercaloric (by definition they had to be to gain weight) and regardless of the change in carbohydrate oxidation because of the difference in total fat and carb consumed there was no difference in fat mass change, because the total Calories consumed were equal.

Even though fat mass changes were equal, does this mean health outcomes were equal? NOPE.

With the very limited provided regarding any plasma variables they indicate in both lean and obese subjects the CHO overfeeding significantly increased fasting plasma insulin concentrations (LEAN- carb overfed = Day 0, 132 pmol/L; Day 15, 207 pmol/L) (LEAN-fat overfed = Day 0, 228 pmol/L; Day 15, 108 pmol/L). All of these values indicate insulin resistance, as a normal fasted insulin value is < 60 pmol/L. Either way the extra carb increased whereas the extra fat decreased insulin in Lean subjects. My thoughts are the Carb overfeeding caused so much insulin resistance that it spiked the Day 0 values for the lean men. Regardless, extra carbs caused insulin raising and  extra fat caused insulin lowering. (OBESE-carb overfed = Day 0, 199 pmol/L; Day 15, 332 pmol/L) (OBESE-fat overfed = Day 0, 172 pmol/L; Day 15, 278 pmol/L). Obese subjects had a rise in fasting insulin no matter what, probably because they were somewhat insulin resistant to begin with. This gets at the concept of "metabolic flexibility", which relates to the muscles being able to use fat when carbs are low and use carbs when carbs are high. Hint: this will also be a topic of another blog post. 

The conclusion of this study? Calories are what seem to matter when it comes to fat mass, but not necessarily with regards to carbohydrate metabolism or potentially health. While not super conclusive, with regards to differences in health it does appear that fasting insulin levels will be significantly higher after overfeeding on carbohydrate. This would suggest that if you are overeating to overeat more on fat than carbohydrate, if insulin is a major concern. 



-Pd. 


Side note: 
Not all people will gain the same amount of fat if they overeat the same Calories. Genetics (and Epigenetics) do play a role in things as does the general phenotype (characteristics and traits based on genetics PLUS environmental and behavioral differences). The type of Calories you eat may alter your propensity to gain or lose fat more or less easily, but when you do gain or lose fat it tends to be from a Calorie surplus or deficit and not the type of Calories.

See: Bouchard, 1990; 322, NEJM. (The Response to Long-Term Overfeeding in Identical Twins).