Here's what SP has to say about target ranges in general: www.sparkpeople.com/resource/nutrition_art
And here's what they say about how the nutrition tracker calculates them: www.sparkpeople.com/resource/calorie_calcu
Note that the two articles are written by Becky Hand, SP's registered dietitian. The working assumption is that they represent official SP policy and that they should be consistent with each other.
Digging through the details, I see that the nutrition tracker supposedly takes your age, weight, height, and gender to compute a Basal Metabolic Rate, applies a multiplier that assumes a sedentary lifestyle, and adds in the calories you told the fitness tracker that you'd burn. Then it subtracts your weight loss burn goal, which is computed based on your current weight, goal weight, and desired date to hit goal. It's rounded up to the nearest 10 calories. Then your range is set at 250 calories less than this target number to 100 calories above it. Ranges for carbs, fat, and protein are set at percentages of the magic calorie number, subject to minimum requirements.
What jumps out at me is that these assumptions won't be appropriate for everyone. Some people won't fall near the sludge average basal metabolic rate that SP uses. If people are actually getting those 10K steps per day in, they aren't sedentary. And I suspect that the tracker actually assumes that everyone is female.*
What does this mean, in practice? Any time you change your weight goal or your fitness plan, the nutrition planner will revise its calculations. Even if the revision comes out to the exact same calorie range as I had before, my minimum protein is reset to the low number SP assigns instead of the higher number I manually put in.
In maintenance, I think you're better off tracking what you eat and seeing how much it takes to hold the weight steady. Then you can manipulate the inputs to generate an appropriate range for the nutrition tracker, if that's your thing. I do this because the fat and carb ranges work well for me, and I can make the protein range work with a single adjustment to the minimum required. The cost of doing this is that the fitness tracker is trash as far as tracking calories. (I think it is anyway, but that's another rant.) Right now, on Saturday, I've logged all the exercise I will log for this week. The fitness tracker says I've burned 2399 calories out of goal of 8600 per week. Why do I have a lofty 8600 calorie exercise burn goal? Because that's what I had to input to get my calorie range where I need it right now for maintenance. There's no way I'm going to do enough stuff that I consider exercise to make the fitness tracker think I've burned 8600 calories in a week.
Bottom line, the nutrition tracker is great for tracking. It's not so great for setting accurate ranges without intervention. The default ranges seem to work for some people, but are too high for some and too low for others. As long as the bias is toward being too low, the SP ranges will support weight loss even for people who "forget" to input a few small things; but the ranges aren't personalized enough to be directly useful for maintenance for people who don't happen to fall close to the average that the calculations are based on.
Oh, and the random change when no inputs were changed? I'm not sure what's going on. I've had my range change on me when I didn't expect it to, but I can't swear that I didn't change any of the inputs. In theory, SP might do this if they revise their calculations; but if that's the case, I'd expect everyone to have their ranges changed at the same time.
* The first article tells me that males need a minimum of 75 grams of protein, but when I was in weight loss mode the nutrition tracker stubbornly set my minimum protein at 60 grams, which is supposed to be the minimum for females. I'm pretty sure I told SP I'm male.
"Discipline is remembering what you want. " - David Campbell
Max Lifetime Weight, 221
SP Start Weight, 196.6
Initial SP Goal, 175
Current Goal on Ticker, 162
| current weight: -0.6 under